Membrane-permeant peptide complexes for medical imaging, diagnostics, and pharmaceutical therapy

ABSTRACT

Methods and compositions for medical imaging, evaluating intracellular processes and components, radiotherapy of intracellular targets, and drug delivery by the use of novel cell membrane-permeant peptide conjugate coordination and covalent complexes having target cell specificity are provided. Kits for conjugating radionuclides and other metals to peptide coordination complexes are also provided.

RELATED U.S. PATENT APPLICATIONS

This application is a continuation-in-part of the application entitledMembrane-Permeant Peptide Complexes For Medical Imaging, Diagnostics,And Pharmaceutical Therapy, filed Feb. 18, 2003, which is a divisionalof Ser. No. 09/557,465, now U.S. Pat. No. 6,589,503 which is acontinuation-in-part of Ser. No. 09/336,093 filed Jun. 18, 1999, nowU.S. Pat. No. 6,348,185 which claims priority to provisional applicationSer. No. 60/090,087 filed Jun. 20, 1998, now abandoned. The contents ofthese applications are incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention broadly relates to the field of medicine. Morespecifically, the present invention relates to the fields of medicalimaging, diagnostics, and pharmaceutical therapy. The present inventionprovides methods and compositions for medical imaging, evaluatingintracellular processes, radiotherapy of intracellular targets, and drugdelivery by the use of novel cell membrane-permeant peptide conjugatecoordination and covalent complexes having target cell specificity. Thepresent invention also provides kits for conjugating radionuclides andother metals to the peptide coordination complexes.

2. Description of Related Art

Radiopharmaceuticals in Diagnosis and Therapy

Radiopharmaceuticals provide vital information that aids in thediagnosis and therapy of a variety of medical diseases (Hom andKatzenellenbogen, Nucl. Med. Biol. 24:485-498, 1997). Data on tissueshape, function, and localization within the body are relayed by use ofone of the various radionuclides, which can be either free chemicalspecies, such as the gas ¹³³Xe or the ions ¹²³I⁻, and ²⁰¹Tl⁻, covalentlyor coordinately bound as part of a larger organic or inorganic moiety,the images being generated by the distribution of radioactive decay ofthe nuclide. Radionuclides that are most useful for medical imaginginclude ¹¹C (t_(1/2) 20.3 min), ¹³N (t_(1/2) 9.97 min), ¹⁵O (t_(1/2)2.03 min), ¹⁸F (t_(1/2) 109.7 min), ⁶⁴Cu (t_(1/2) 12 h), ⁶⁸Ga (t_(1/2)68 min) for position emission tomography (PET) and ⁶⁷Ga (t_(1/2) 68min), ^(99m)Tc (t_(1/2) 6 h), ¹²³I (t_(1/2) 13 h) and ²⁰¹Tl (t_(1/2)73.5 h) for single photon emission computed tomography (SPECT) (Hom andKatzenellenbogen, Nucl. Med. Biol. 24:485-498, 1997).

SPECT and PET imaging provide accurate data on radionuclide distributionat the desired target tissue by detection of the gamma photons thatresult from radionuclide decay. The high degree of spatial resolution ofmodem commercial SPECT and PET scanners enables images to be generatedthat map the radionuclide decay events into an image that reflects thedistribution of the agent in the body. These images thus containanatomic and functional information useful in medical diagnosis.Similarly, if the radionuclides decay in such a manner as to depositradiation energy in or near the target cells or tissues, the sameapproach would enable therapeutically relevant doses of radioactivity tobe deposited within the tissues.

Many radiopharmaceuticals have been prepared whose tissue localizingcharacteristics depend on their overall size, charge, or physical state(Hom and Katzenellenbogen, Nucl. Med. Biol. 24:485-498, 1997). Otherradiopharmaceuticals are synthesized with the intention to be ligandsfor specific hormone, neurotransmitter, cell surface or drug receptors,as well as specific high affinity transport systems or enzymes. As thesereceptors and enzymes are known to be involved in the regulation of awide variety of vital bodily functions, effective imaging agents can beused in the diagnosis or staging of a variety of disease states, inwhich such receptors are functioning abnormally or are distributed in anabnormal fashion, or in the monitoring of therapy (Hom andKatzenellenbogen, Nucl. Med. Biol. 24:485-498, 1997). Effectivetherapeutic agents can also be used to deliver pharmacologically activedoses of compounds to the same receptors and enzymes.

Recent advances in molecular, structural and computational biology havebegun to provide insights in the structure of receptors and enzymes thatshould be considered in the design of various ligands. Two key issuesderived from the structure and distribution of these receptors have adirect impact on the development of new radiopharmaceuticals: 1) thelocation of a receptor or enzyme activity in the body (i.e., peripheralsites versus brain sites), and 2) its subcellular location (i.e., on thecell surface versus intracellular) will determine whether aradiopharmaceutical injected intravenously will need to traverse zero,one, two or more membrane barriers to reach the target. The structure ofthe receptor and the nature of its interaction with the ligand willdetermine the degree to which large ligands or ligands with largesubstituents may be tolerated (Hom and Katzenellenbogen, Nucl. Med.Biol. 24:485-498, 1997). For example, radiopharmaceuticals which targetcell surface receptors will encounter no membrane barriers to reachtheir target. Natural ligands for these receptors can be large, andoften are charged and, consequently, large radiopharmaceuticals aretolerated. Conversely, for a radiopharmaceutical to reach intracellularreceptors or enzymes, at least one membrane barrier, the cell plasmamembrane, must be traversed, and if the target site is within thecentral nervous system, the radiopharmaceutical must also traverse theplasma membranes of endothelial cells of the brain which constitute theblood-brain barrier. Such a situation usually favors radiopharmaceuticaldesigns that strongly minimize ligand size and molecular weight (Hom andKatzenellenbogen, Nucl. Med. Biol. 24:485-498, 1997). Thus, as thenumber of membrane barriers increases, a premium is placed on keepingthe size of a conventional radiopharmaceutical small (<600 Da) and thelipophilicity intermediate (characterized by an octanol-water partitioncoefficient, log P ˜2) to enable the agent to traverse membranes(Dishino, et al., J Nucl Med 24: 1030-1038, 1983; Papadopoulos, et al.,Nucl Med Biol 20:101-104, 1993; Eckelman, Eur J Nucl Med 22:249-263,1995). This has conventionally precluded the use of peptideradiopharmaceuticals for intracellular targets.

There has been a great deal of research into the development ofradiopharmaceuticals directed toward cell surface receptors whosenatural ligands are peptides. Tc-labeled peptides can span the spectrumof size. The derivatizing group or chelation core of smaller peptideshas been reported to impact the in vitro binding and in vivodistribution properties of these compounds (Babich and Fischman, NuclMed Biol 22:25-30, 1995; Liu, et al., Bioconj Chem 7:196-202, 1996). Forlarger peptides or proteins, the labeling process can usually occur atone or more of several reactive sites, and thus, the final mixture ofcompounds is less chemically defined. Thus, for larger proteins, it isusually much less clear which of these sites, if any, might be morefavorable for receptor interaction and whether or not specific labelingwould increase biological activity of the agent (Hom andKatzenellenbogen, Nucl. Med. Biol. 24:485-498, 1997).

It is known that low molecular weight peptides and antibody fragmentsprovide rapid tumor targeting and uniform distribution in tumor tissues(Yokota et al., Cancer Res 53:3776-3783, 1993). While suchcharacteristics render low molecular weight peptides attractive vehiclesfor the delivery of radioactivity to tumor tissues and organs for bothtargeted imaging and radiotherapy, nonetheless problems have beenencountered. High and persistent localization of the radioactivity isobserved in the kidneys, which compromises tumor visualization in thekidney region and limits therapeutic potential (Buijs, et al., J NuclMed 33:1113-1120, 1992; Baum, et al., Cancer (Phila) 73:896-899, 1994;Choi, et al., Cancer Res 55:5323-5329, 1995; Behr, et al., J Nucl Med36:430-441, 1995). As discussed by Arano, et al. (Cancer Res 59:128-143,1999), radiolabeled low molecular weight peptides and antibody fragmentswould become much more useful for targeted imaging and therapy if therenal radioactivity levels could be reduced without impairing those inthe target tissue. Previous studies have indicated that radiolabeled lowmolecular weight peptides and antibody fragments are likely resorbed byproximal tubules via luminal endocytosis after glomerular filtration(Silberbagl, S. Physiol Rev 68:811-1007, 1988). The long residence timesof the radiometabolites generated after lysosomal proteolysis of theradio labeled fragments in renal cells were also reported to beresponsible for the persistent renal radioactivity levels (Choi, et al.,Cancer Res 55:5323-5329; Rogers, et al., Bioconjugate Chem7:511-522,1996).

There exists a continued need for peptide-based radiopharmaceuticalsthat are rapidly cleared and target intracellular receptors or enzymeactivities.

Peptide-Based Metal Coordination Complexes

Small peptides can be readily prepared by automated solid phase peptidesynthesis (Merifield et al., Biochemistry 21:5020-5031, 1982; Houghten,Proc Natl Acad Sci USA 82:5131-5135, 1985; Lin, et al., Biochemistry27:5640-5645, 1988) using anyone of a number of well known, commerciallyavailable automated synthesizers, such as Applied Biosystems ABI 433Apeptide synthesizer. Many combinations of natural and non-natural aminoacids and peptide sequence mimetics (peptidomimetics) are possible, andselective engineering of favorable target-binding and pharmacokineticproperties can be accomplished with natural and unnatural peptides(Lister-James et al., Q. J: Nucl. Med., 41:111-118, 1997).Peptidomimetics are unnatural biopolymers that do not contain α-aminoacids, but rather incorporate backbone structures with hydrogen-bondinggroups (such as urea), chiral centers, side chain functionalities, and asufficient degree of conformational restriction to behave similar to, ormimic the bioactivities of, a natural polypeptide. Peptide-based imagingagents are also well known (Lister-James et al., Q. J: Nucl. Med.,41:111-118,1997; Lister-James et al., J. Nucl. Med., 38:105-111, 1997),especially those that incorporate Tc-99m as the radionuclide, the mostcommonly used isotope in medical imaging.

The metallic character of Tc-99m requires that it be stabilized by achelation system to be coupled to an imaging agent. This chelator maytypically involve a multiple heteroatom coordination system, or theformation of a non-labile organometallic species. There are two broadstrategies for binding metals for biological applications. These are“the pendant approach” and “the integrated approach,” which have beenrecently reviewed by Katzenellenbogen and colleagues (Hom andKatzenellenbogen, Nucl. Med. Biol., 24:485-498, 1997). The pendant (orconjugate) approach involves the strategic placement of aTc-99m-chelator-tether moiety at a site on the ligand that will nothinder binding of the ligand to its high affinity receptor. Theintegrated approach replaces a component of a known high-affinityreceptor ligand with the requisite Tc-99m chelator such that there is aminimal change in the size, shape, structure, and binding affinity ofthe resultant molecule. Applications involving peptide-based imagingagents typically use the conjugate design, whereby an appropriate metalchelating moiety is affixed to the amino or carboxy terminus of thetargeting peptide.

A variety of metal chelation systems have been developed for synthesisof radioisotopic and magnetic resonance peptide-based imaging agents.Peptide-based agents target extracellular or externally orientedmembrane bound receptors (Hom and Katzenellenbogen, Nucl. Med. Biol.,24:485-498, 1997) because the charge, size, and pharmacokineticproperties of typical peptide structures do not allow diffusion acrossthe lipid bilayer of the cell plasma membrane. This limitation hasprevented peptide metal chelates from reporting the functional status orbiological activity of intracellular receptors or enzymes or otherhomeostatic activities and intracellular targets. Although techniquesand reagents for labeling antibodies and antibody fragments withmetal-chelates are well known in the art (Hom and Katzenellenbogen,Nucl. Med. Biol., 24:485-498, 1997, and references therein), they targetextracellular or externally oriented cell surface receptors.

Tat Proteins and Peptides

Tat is an 86-amino acid protein involved in the replication of humanimmunodeficiency virus type 1 (HIV-1). The HIV-1 Tat transactivationprotein is efficiently taken up by cells (Mann and Frankel, EMBO,10:1733-1739, 1991; Vives et al., J. Virol., 68:3343-3353, 1994), andlow concentrations (nM) are sufficient to transactivate a reporter geneexpressed from the HIV-1 promoter (Mann and Frankel, EMBO, 10:1733-1739,1991). Exogenous Tat protein is able to translocate through the plasmamembrane and reach the nucleus to transactivate the viral genome(Frankel and Pabo, Cell 55:1189-1193, 1988; Ruben, et al, J Virol63:1-8, 1989; Garcia, et al., EMBO J 7:3143, 1988; Jones, Genes Dev11:2593-2599,1997).

A region of the Tat protein centered on a cluster of basic amino acidsis responsible for this translocation activity (Vives et al., J Biol.Chem., 272:16010-16017, 1997). Tat peptide-mediated cellular uptake andnuclear translocation have been demonstrated in several systems (Vives,et al., J Biol Chem 272:16010-16017, 1997; Jones, Genes Dev11:2593-2599, 1997). Chemically coupling a Tat-derived peptide (residues37-72) to several proteins results in their internalization in severalcell lines or tissues (Fawell, et at, Proc Natl Acad Sci USA 91:664-668,1994; Anderson, et at, Biochem Biophys Res Commun 194:876-8884, 1993;Fahraeus, et al., Curr Biol 6:84-91, 1996; Nagahara, et al, Nat Med4:1449-1452, 1998). A synthetic peptide consisting of the Tat basicamino acids 48-60 with a cysteine residue at the C-terminus coupled tofluorescein maleimide translocates to the cell nucleus as determined byfluorescence microscopy (Vives et al., J. Biol. Chem., 272:16010-16017,1997). In addition, a fusion protein (Tat-NLS-β-Gal) consisting of Tatamino acids 48-59 fused by their amino-terminus to β-galactosidase aminoacids 9-1023 translocates to the cell nucleus in an ATP-dependent,cytosolic factor-independent manner (Efthymiadis et al., J. Biol. Chem.,273:1623-1628, 1998).

While the literature teaches that Tat peptide constructs and similarmembrane permeant peptides readily translocate into the cytosolic andnuclear compartments of living cells, little is known regarding thecellular retention characteristics over time once the permeant peptideconstructs are no longer in contact with the cell surface from theextracellular fluid spaces. Furthermore, no information is availableregarding the pharmacokinetic and distribution characteristics ofmembrane-permeant peptides within a whole living organism, animal orhuman.

Apoptosis

Chemotherapeutic drugs used in the treatment of cancer are thought tointeract with diverse cellular targets in conferring lethal effects onmammalian cells. Recently, anticancer agents, irrespective of theirintracellular target, have been shown to exert their biological effectin target cells by triggering a common final death pathway known asapoptosis (Fulda, et al., Cancer Res 57:3823-3829,1997; Fisher, Cell78:539-542, 1994). Thus, there exists mounting evidence that manyanticancer treatments may kill through apoptosis by activatingintracellular death machinery in the target cell rather than by simplycrippling various components of cellular metabolism (Fulda, et al.,Cancer Res 57:3823-3829,1997; Fisher, Cell 78:539-542, 1994). In fact,the action of ionizing radiation, drug therapy, and withdrawal ofphysiological survival factors all appear to act as death stimuli inpromoting execution of this common apoptotic pathway (Evan andLittlewood, Science 281:1317-1322, 1998; Ashkenazi and Dixit, Science281:1305-1308, 1998). Thus, new models of resistance to therapy havebegun to focus on mechanisms that antagonize execution of the apoptoticpathway.

Apoptotic stimuli can arise from the nucleus, cell membrane surface, orthe mitochondria (Wyllie, Nature, 389:237-38, 1997). Ultimately, thestimuli converge on a process of activation of a family of interleukin1β-converting enzymes {(ICE)-like cysteine proteases} known as cysteineaspartases (“caspases”) (Thornberry et al., Science, 281:1312-16, 1998).Members of the caspase family are activated in apoptosis and have beenshown to be necessary for programmed cell death in a number ofbiological systems (Yuan et al., Cell, 75:641-52, 1993; Thornberry etal., Science, 281:1312-16,1998). The caspase gene family, defined bysequence homology, is also characterized by conservation of keycatalytic and substrate-recognition amino acids (Talanian et al., J.Biol. Chem., 272:9677-82, 1997). Thirteen mammalian caspases (1 through13) have thus far been isolated, having distinct roles in apoptosis andinflammation (Thornberry et al., Science, 281:1312-16, 1998). Inapoptosis, some caspases are involved in upstream regulatory events andare known as “initiators,” while others are directly responsible forproteolytic cleavages that lead to cell disassembly and are known as“effectors.” Evidence indicates that caspases transduce or amplifysignals by mutual activation. For example, Fas-induced apoptosis ischaracterized by an early, transient caspase-1-like protease activityfollowed by a caspase-3-like activity, suggesting an ordered activationcascade (Enari et al., Nature, 380:723-26, 1996). Other data suggestthat both caspase-3 and caspase-7 are activated by caspase-6 andcaspase-10 (Thornberry et al., Science, 281:1312-16, 199;Fernandes-Alnemri, Proc. Natl. Acad. Sci. USA, 93:7464-69, 1996). Thus,while the activation cascade hypothesis remains to be absolutely proven(Villa et al., Trends in Biochem. Sci., 22:388-93, 1997), circumstantialevidence strongly points to caspase-3 as one key “effector” caspase,standing at the center of the execution pathway of the cell deathprogram.

Caspases are some of the most specific of the proteases, showing anabsolute requirement for cleavage after aspartic acid (Thornberry etal., Science, 281:1312-16, 1998). Recognition of at least four aminoacids, amino terminal to the cleavage site, is also necessary forefficient catalysis. The preferred recognition motif differssignificantly between caspases, thereby contributing to theirbiologically diverse functions (Talanina et al., J. Biol. Chem.272:9677-82, 1997). In addition to high specificity, caspases are alsohighly efficient, with K_(cat)/K_(m) values >10⁶ M⁻¹s⁻¹ (Thornberry etal., Science, 281:1312-16, 1998). When viewed from the perspective of amolecular target for oncological imaging, this is a key property of thecaspases that allows detection of caspase activity in vivo byradiosubstrates. Another advantage of the caspases as imaging targetscenters on the nature of the biochemical reaction. Because normal cellshave essentially non-detectable levels of caspase activity, and onceactivated, the “caspase cascade” amplifies reaction rates to maximalvelocities (Thornberry et al., Science, 281:1312-16, 1998), the signalreadout obtained by imaging is binary in character. That is, in theabsence of caspase activity, the imaging signal will be low, and whenactivated, a highly amplified imaging signal will result. This rendersthe caspase-mediated enzymatic reaction essentially zero-order in situand, therefore, independent of radiotracer concentration or specificactivity, thus eliminating the complexities of first or higher orderreaction rates.

Deregulation of apoptosis resulting in insufficient cell death can occurin cancer, allowing malignant tissues to grow (Thornberry et al.,Science, 281:1312-16, 1998). Conversely, some diseases involve excessapoptosis, such as neurodegenerative disease, ischemia-reperfusion,graft-vs-host disease, and autoimmune disorders (Thornberry et al.,Science, 281: 1312-16, 1998). Accordingly, two-fold strategies fortherapeutic intervention are actively underway within the pharmaceuticalindustry, one to selectively induce apoptosis through caspaseactivation, the other to inhibit caspase activity. In order to assessthe treatments to alter apoptosis, an accurate means to assess apoptoicactivity in vivo is needed.

Inactive pro-caspases are constitutively expressed as pro-enzymes innearly all cells, existing in latent forms in the cell cytoplasm (Villaet al., Trends in Biochem. Sci. 22:388-93, 1997). Thus, while caspase-3can be readily identified by Western blots, this requires biopsymaterial and lysis of the cells. Furthermore, activation of caspase-3 isonly inferred by observation of lower molecular weight cleavagefragments on the blot. Activation of caspase-3 has also been inferredfrom nuclear shifts of antigen by immunohistochemical analysis of biopsymaterial and shown to be associated with a more favorable prognosis in,for example, pediatric neuroblastoma (Nakagawara et al., Cancer Res.57:4578-84, 1997). However, these indirect methods only implyactivation. Thus, the simple determination of the presence or absence ofcaspase proteins is not necessarily diagnostically useful. A method todirectly and non-invasively detect and quantify the enzymatic activityof caspases in order to monitor the commitment to cell death pathway isneeded. Because caspases are cytosolic enzymes, new diagnostic andtherapeutic compounds are required that can readily cross cellmembranes, and whose specificity is based on the presence of proteaseactivity.

Tat Peptide Complexes

Frankel et al. (U.S. Pat. Nos. 5,804,604; 5,747,641; 5,674,980;5,670,617; 5,652,122) discloses the use of Tat peptides to transportcovalently linked biologically active cargo molecules into the cytoplasmand nuclei of cells. Frankel only discloses covalently linked cargomoieties, and does not teach or suggest the attachment of metals to Tatpeptides by metal coordination complexes. Specifically, Frankel does notteach the use of peptide chelators to introduce radioimaging materialsinto cells. In addition, while Frankel teaches the use of cleavablecoupling reagents between the Tat protein and the cargo molecule, thecleavable linkers disclosed are non-specific, such that the retention ofthe cargo molecule is not limited to specific cells.

Anderson et al. (U.S. Pat. Nos. 5,135,736 and 5,169,933) discloses theuse of covalently linked complexes (CLCs) to introduce molecules intocells. CLCs comprise a targeting protein, preferably an antibody, acytotoxic agent, and an enhancing moiety. Specificity is imparted to theCLC by means of the targeting protein, which binds to the surface of thetarget cell. After binding, the CLC is taken into the cell byendocytosis and released from the endosome into the cytoplasm. In oneembodiment, Anderson discloses the use of the Tat protein as part of theenhancing moiety to promote translocation of the CLC from the endosometo the cytoplasm. In another embodiment, Anderson discloses the use ofCLCs to transport radionuclides useful for imaging into cells. Thecomplexes described by Anderson are limited in their specificity tocells that can be identified by cell surface markers. Many biologicallyand medically significant cellular processes, for example caspaseprotease activities discussed above, are not detectable with cellsurface markers. In addition, the attachment of enhancing moieties tothe CLC is accomplished by the use of bifunctional linkers. The use ofbifunctional linkers results in the production of a heterogeneouspopulation of CLCs with varying numbers of enhancing moieties attachedat varying locations. This can lead to the production of CLCs in whichthe biological activity of the targeting protein, the enhancing moiety,or both, are lost. Another disadvantage of CLCs is that the number andlocation of linked enhancing moieties will vary with each reaction, sothat a consistent product is not produced.

There is a need in the art for cell membrane-permeant peptide complexesof uniform composition, capable of delivering radionuclides, othermetals, diagnostic substances such as fluorochromes, dyes, etc., andtherapeutic and cytotoxic drugs into cells in a specific and selectivemanner. Furthermore, rapid clearance of the complexes from non-targetcells and tissues of the body would facilitate and enhance the utilityof such complexes in vivo.

SUMMARY OF THE INVENTION

The present inventor has surprisingly discovered that the addition ofD-amino acid containing membrane-permeant peptides attached to non- orpoorly permeant drugs, diagnostic and/or therapeutic substances such asoligonucleotides, peptides, peptide nucleic acids, fluorochromes, dyes,enzyme substrates, and metals useful in medical therapy, imaging, and/ordiagnostics greatly increases their accumulation within cells. As shownin Example 14, this increase in accumulation is on the order of 8- to9-fold as compared to membrane-permeant peptides comprising onlynaturally occurring L-amino acids. Thus, use of the D-amino acidcontaining membrane-permeant peptides of the present invention allowsdelivery of greater amounts of therapeutic or diagnostic substances tothe interior of cells either in vivo or in vitro than was heretoforepossible using membrane permeant peptides containing only L-amino acids.

The present inventor has also discovered that the Tat peptide and othercell membrane-permeant peptides can be used to selectively deliver non-or poorly permeant drugs, diagnostic and/or therapeutic substances suchas oligonucleotides, peptides, peptide nucleic acids, fluorochromes,dyes, enzyme substrates, and metals useful in medical therapy, imaging,and/or diagnostics selectively to cells in vivo only when functionallinkers are introduced into the permeant peptide construct, and hasdeveloped methods for linking these substances to Tat and other peptidesfor use in such methods. As illustrated in Examples 6 and 10, below,non-targeted Tat peptides, rather than being trapped inside cells andtissues indefinitely, are cleared surprisingly rapidly from body tissueswhen introduced into the living organism. Furthermore,non-functionalized prototypes of such complexes are rapidly excreted bythe kidneys and cleared from the whole body. Thus, membrane-permeantpeptides covalently linked to oligopeptides, proteins, oligonucleotides,and drugs as known previously possess rapid and ineffective biologicalhalf-times within the whole organism.

Thus, in response to this surprising and unanticipated property ofD-amino acid containing permeant peptides and to improve upon the priorart, the present invention provides novel permeant peptide conjugates,complexes and methods that possess the advantage of enabling thetargeted trapping of greater amounts of such compounds or fragmentsthereof within desired cells, tissues and organs of the intact body ofliving organisms. Conversely, when it is desired to increase the ratesof clearance of cargo oligopeptides, proteins, oligonucleotides, metals,and drugs, the present invention also provides methods that will enhancetheir rates of clearance from the body.

Accordingly, in a first aspect, the present invention provides acompound comprising a cell membrane-permeant peptide; a diagnostic orpharmaceutically active substance; and a functional linker moietylinking the peptide and the diagnostic or pharmaceutically activesubstance, wherein the compound further comprises at least one D-aminoacid and the functional linker moiety confers target cell specificity tothe compound, or a pharmaceutically acceptable salt of the compound.

In a second aspect, the present invention provides a compositioncomprising, a compound comprising a cell membrane-permeant peptide; adiagnostic or pharmaceutically active substance; and a functional linkermoiety linking the peptide and the diagnostic or pharmaceutically activesubstance, wherein the compound further comprises at least one D-aminoacid and the functional linker moiety confers target cell specificity tothe compound. The composition can further comprise a pharmaceuticallyacceptable carrier, excipient, or diluent.

In a third aspect, the present invention provides a kit comprising, acompound comprising a cell membrane-permeant peptide; a metal chelationligand; and a functional linker moiety linking the peptide and the metalchelation ligand, wherein the compound further comprises at least oneD-amino acid and the functional linker moiety confers target cellspecificity to the compound, and a reducing agent capable of reducing ametal that can be coordinately incorporated into the metal chelationligand.

In another aspect, the present invention provides a method for imagingcells in vivo, comprising administering to an animal a cell imagingeffective amount of a compound comprising a cell membrane-permeantpeptide; a chelated radionuclide or a chelated relaxivity metal; and afunctional linker moiety linking the peptide and the chelatedradionuclide or the chelated relaxivity metal, the functional linkerconfering target cell specificity to the compound, and monitoring orevaluating the location of the radionuclide or relaxivity metal withinthe animal. Further the compound may comprise at least one D-amino acid.

In another aspect, the present invention provides a method for imagingcells in vitro, comprising contacting the cells with a cell imagingeffective amount of a compound comprising a cell membrane-permeantpeptide; a diagnostic substance; and a functional linker moiety linkingthe peptide and the diagnostic substance, wherein the functional linkerconfers target cell specificity to the compound, and monitoring orevaluating the presence of the diagnostic substance within the cells.Further, the compound may comprise at least one D-amino acid.

In a further aspect, the present invention provides a method fordetecting cellular apoptosis in vivo, comprising administering to ananimal a cellular apoptosis detecting effective amount of a compoundcomprising a cell membrane-permeant peptide; a diagnostic substance; anda functional linker moiety linking the peptide and the diagnosticsubstance, wherein the functional linker moiety comprises acaspase-reactive sequence, and monitoring the diagnostic substancewithin the animal. Further, the compound may contain at least oneD-amino acid.

In another aspect, the present invention provides a method for detectingcellular apoptosis in vitro, comprising contacting cells or tissue invitro with a cellular apoptosis detecting effective amount of a compoundcomprising a cell membrane-permeant peptide; a diagnostic substance; anda functional linker moiety linking the peptide and the diagnosticsubstance, wherein the functional linker moiety comprises acaspase-reactive sequence, and monitoring the diagnostic substancewithin the cells or tissue. Further, the compound may contain at leastone D-amino acid.

In yet another aspect, the present invention provides a method fordetecting an enzyme in a cell, comprising contacting the cell with anenzyme detecting effective amount of a compound comprising a cellmembrane-permeant peptide; a diagnostic substance; a functional linkermoiety linking the peptide and the diagnostic substance, wherein thefunctional linker moiety comprises a sequence reactive with the enzyme;removing unreacted compound from the locus of the cell so that thesignal to noise ratio is sufficient for diagnostic purposes; andmonitoring the presence of the diagnostic substance in the cell. Suchmonitoring can be performed quantitatively, and the cell can be presentwithin a living animal. Furthermore, the enzyme can be one that ischaracteristically associated with a disease, condition, or disorder.Further, the compound may contain at least one D-amino acid.

In yet another aspect, the present invention provides a method fordiagnosing the presence of a disease, condition, or disorder in ananimal, comprising administering to the animal a diagnosticallyeffective amount of a compound comprising a cell membrane-permeantpeptide; a diagnostic substance; a functional linker moiety linking thepeptide and the diagnostic substance, wherein the functional linkermoiety confers target cell specificity to the compound, and whichcomprises a sequence reactive with an enzyme indicative orcharacteristic of the disease, condition, or disorder, and monitoringthe diagnostic substance within the animal. By way of example, thedisease, condition, or disorder can be a cancer such as a centralnervous system tumor, breast cancer, liver cancer, lung cancer, headcancer, neck cancer, a lymphoma, or a melanoma. Further, the compoundmay contain at least one D-amino acid.

In still another aspect, the present invention provides a method ofassessing the effectiveness of cancer therapy, comprising administeringto an animal undergoing cancer therapy a diagnostically effective amountof a compound comprising a cell membrane-permeant peptide; a diagnosticsubstance; and a functional linker moiety linking the peptide and thediagnostic substance, wherein the functional linker moiety conferstarget cell specificity to the compound, and which comprises acaspase-reactive sequence, and monitoring the diagnostic substancewithin the animal. Such monitoring can be performed quantitatively.Furthermore, the method can be repeated at intervals during the cancertherapy, and the quantity of the diagnostic substance detected withinthe animal at each interval can be compared to the quantity of thediagnostic substance detected at previous intervals to determine theeffectiveness of the therapy. In addition, the compound may contain atleast one D-amino acid.

In yet another aspect, the present invention provides a method ofdelivering a pharmaceutically active substance to a cell, comprisingcontacting the cell with an effective amount of a compound comprising acell membrane-permeant peptide; a pharmaceutically active substance; anda functional linker moiety linking the peptide and the pharmaceuticallyactive substance, wherein the compound further comprises at least oneD-amino acid and the functional linker moiety confers target cellspecificity to the compound.

In another aspect, the present invention provides a method of treating,inhibiting, or preventing a disease, condition, or disorder responsiveto treatment with a pharmaceutically active substance in an animal,comprising administering to the animal a pharmaceutically effectiveamount of a compound comprising a cell membrane-permeant peptide; apharmaceutically active substance; and a functional linker moietylinking the peptide and the pharmaceutically active substance, whereinthe compound further comprises at least one D-amino acid and thefunctional linker moiety confers target cell specificity to thecompound.

In another aspect, the present invention provides a method forselectively destroying cells expressing a selected enzyme activity,comprising contacting the cells with a cell-destroying effective amountof a compound comprising a cell membrane-permeant peptide; a cytotoxicsubstance; and a functional linker moiety linking the peptide and thecytotoxic substance, wherein the compound further comprises at least oneD-amino acid and the functional linker moiety confers target cellspecificity to the compound.

In yet another aspect, the present invention provides a method forassessing the effect of a drug in altering the expression or activity ofan enzyme in a target cell, comprising contacting the target cell with adiagnostically effective amount of a compound comprising a cellmembrane-permeant peptide; a diagnostic substance; a functional linkermoiety linking the peptide and the diagnostic substance, wherein thefunctional linker moiety confers target cell specificity to thecompound, and which comprises a sequence capable of interacting with theenzyme so as to release the diagnostic substance from the compound intothe interior of the cell; clearing unreacted compound from the locus ofthe cell so that the signal to noise ratio is sufficient for diagnosticpurposes; and monitoring or evaluating the diagnostic substance in thetarget cell. Such monitoring can be performed quantitatively, and thetarget cell can be present within a living animal. Furthermore, theenzyme can be associated with a disease, condition, or disorder. Inaddition, the compound may further comprise at least one D-amino acid.

In yet another aspect, the present invention provides a method fordetecting the expression of a nucleic acid sequence, which can be DNA orRNA, encoding an enzyme, a receptor, or a binding protein introducedinto a cell, comprising contacting the cell with a compound comprising acell membrane-permeant peptide; a diagnostic substance; a functionallinker moiety linking the peptide and the diagnostic substance, whereinthe functional linker moiety confers target cell specificity to thecompound, and which comprises a sequence capable of interacting with theenzyme, receptor, or binding protein so as to selectively retain thediagnostic substance in the cell, and monitoring the diagnosticsubstance in the cell. Further, the compound may comprise at least oneD-amino acid.

Further scope of the applicability of the present invention will becomeapparent from the detailed description and drawings provided below.However, it should be understood that the following detailed descriptionand examples, while indicating preferred embodiments of the invention,are given by way of illustration only since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will be better understood from the following detaileddescription taken in conjunction with the accompanying drawings, all ofwhich are given by way of illustration only, and are not limitative ofthe present invention, in which:

FIG. 1 shows the general structure of a cell membrane-permeant peptidecoordination complex of the present invention.

FIG. 2 shows the proposed structure of an oxotechnetium-Tat-peptidecomplex. The coordination metal (Tc^(v)O) may be replaced by Re^(v)O toform essentially isostructural complexes.

FIG. 3 shows the time course of cellular uptake of a Tc-99m-Tat peptidecomplex in human Jurkat cells. Extracellular concentration of peptidewas 950 nM. Each point represents the mean of 4 observations±SEM whenlarger than the symbol. Cell accumulation of the Tc-99m-Tat peptidecomplex is 90% complete within 2 minutes and established a quasi-steadystate that was maintained for at least 1 hour (data not shown).

FIG. 4 shows the concentration-dependence of plateau accumulation ofTc-99m-Tat peptide conjugate into human Jurkat cells. Each pointrepresents the mean of 4 observations±SEM when larger than the symbol.

FIG. 5 shows washout kinetics of a non-functional Tc-99m-Tat peptidecomplex from human Jurkat cells. Cells were loaded to plateau uptake(˜30 min), washed in ice cold buffer to clear extracellular spaces, andthen bathed in isotope-free buffer at 37° C. for the times indicated.Cell-associated counts are shown. Each point represents the mean of 4observations±SEM when larger than the symbol.

FIG. 6 shows the cellular accumulation of Tat peptide chelate conjugatesin KB-3-1 human tumor cells. KB-3-1 cells were incubated with compoundfor 15 min at room temperature followed by a rapid wash and fixation:fluorescein maleimide (0.5 μM) alone (left) or Tat peptidechelate-fluorescein maleimide conjugate (right). Tat peptide chelate wasconjugated with fluorescein maleimide on the C-terminal Cys residue.There was no counter staining of nuclei with propidium iodide in thisexample. Note the distribution of fluorescence from labeled peptideconjugate corresponding to cytosolic and nuclear (nucleolar)distribution. Bar=5 μm.

FIG. 7 shows RP-HPLC traces (440 nm) of cell lysates from controluntreated Jurkat cells without added Tat peptide (A), untreated Jurkatcells incubated in fluorescein tagged Tat peptide (B), andceramide-treated caspase-3 activated cells incubated in fluoresceintagged Tat peptide (C). The intact fluorescein tagged Tat peptide isseen in tracing B (arrow at R_(t)=33.5 min). In tracing C, note theabsence of the intact Tat peptide. All three tracings showautofluorescent compounds present in the cells at R_(t)=22 and 28 min.

FIG. 8 shows scintigraphic image of rapid renal excretion of aTc-99m-Tat peptide in a normal FVB mouse 30 minutes post injection.Following metofane anesthesia, Tc-99m-Tat chelate (200 μCi, prepared asdescribed in the application) was administered by tail vein injectionand the mouse immediately positioned for imaging on a gammascintillation camera (Siemens Basicam; 5 mm pinhole collimator; 20%energy window centered over 140 keV). Sequential posterior images of themouse were collected at one frame/minute for ˜30 min with a 128×128matrix. A [mal 5 minute acquisition with a 256×256 matrix was alsoobtained. Images were corrected for radioactive decay, but nocorrections were made for scatter or attenuation. While radioactivityinitially distributed throughout the body, note focal radioactivitywithin the urinary bladder after only 30 minutes, reflecting rapid renalexcretion of the Tat peptide conjugate.

FIG. 9 shows scintigraphic images of organ distribution ofcaspase-3-cleavable Tc-99m-Tat peptide in FVB mice 30 minutes postinjection. Using a published procedure (Blankenberg, et al., Proc NatlAcad Sci USA 95:6349-6354, 1998), FVB mice were administered purifiedhamster anti-Fas mAb (Jo2, PharMingen; 8 μg/animal) by i.v. injectionand allowed to recover for 45 minutes prior to imaging. Followingmetofane anesthesia, Tc-99m-Tat chelate (200 μCi, prepared as describedin the text) was administered by tail vein injection and miceimmediately positioned for imaging on a gamma scintillation camera(Siemens Basicam; 5 mm pinhole collimator; 20% energy window centeredover 140 keV). Sequential posterior images of mice were collected at oneframe/minute for ˜30 min with a 128×128 matrix. A final 5 minuteacquisition with a 256×256 matrix was also obtained. Images werecorrected for radioactive decay, but no corrections were made forscatter or attenuation. Left, untreated control mouse; right, mousepre-treated with anti-Fag mAb. Note focal radioactivity only in theurinary bladder of the control mouse, but abundant retention ofradioactivity in the pre-treated animal within the liver and kidneys,two organs that express the Fas receptor wherein caspase-mediatedapoptosis is induced and imaged.

FIG. 10 shows comparative uptake of D, L and mixed D/L[^(99m)Tc]Tat-peptide chelate conjugates. Net, 20 minute accumulationvalues into Jurkat cells are shown. Each bar represents the mean of 4observations+SEM. (1) L/L, [^(99m)Tc]Tat-peptide conjugate 2; (2) L/D[^(99m)Tc]Tat-peptide conjugate 5; (3) D/D [^(99m)Tc]Tat-peptideconjugate 9; and (4) D/L [^(99m)Tc]Tat-peptide conjugate 12.

FIG. 11 shows net cell uptake of permeation peptides with varyinglengths of the permeation sequence. Radiolabeled peptides were incubatedwith Jurkat cells as described in FIG. 1 and Methods. A=D Tat basicdomain (13-17), B=D amphipathic cationic peptide (18-21), C=L poly-Argpeptide (26, 28, 30, 32), D=D poly-Arg peptide (27, 29, 31, 33); (▪) 9residues in permeation sequence, (□) 8 residues, (vertical lines) 7residues, (horizontal lines) 6 residues, (checkered lines) 5 residues.

FIG. 12A shows the effect on Jurkat cell uptake of substitutingdifferent amino acids for Gln in Tat basic domain (RKKRRXRRR); X=Glu,24; Gln, 7; Asn, 22; Norleu, 25; and Orn, 23. FIG. 12B shows the effecton Jurkat cell uptake of a single substitution in poly-Arg₈ peptide(RRRRXRRR); X=Arg, 31; Orn, 35; Norleu, 37; Asn, 34; Glu, 36.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is provided to aid those skilled inthe art in practicing the present invention. Even so, this detaileddescription should not be construed to unduly limit the presentinvention as modifications and variations in the the embodimentsdiscussed herein can be made by those of ordinary skill in the artwithout departing from the spirit or scope of the present inventivediscovery.

All publications, patents, patent applications and other referencescited in this application are herein incorporated by reference in theirentirety as if each individual publication, patent, patent applicationor other reference were specifically and individually indicated to beincorporated by reference.

As used herein, the term “animal” includes, but is not limited to,mammals, including human beings. It should be noted that the complexesand methods disclosed herein are applicable in both human and veterinarymedicine. Thus, the present compounds and methods can be applied tohumans, domestic pets such as cats, dogs, rodents, birds etc., farmanimals such as cows, sheep, goats, pigs, horses, etc., zoo animals,etc.

Amino acids are indicated herein using the single letter notationconventional in the art. When used in amino acid sequences, the letter“x” designates any amino acid. When used in an amino acid sequence, a“/” between two adjacent letters indicates that either of the aminoacids listed can be used. When used in nucleotide sequences, the letter“n” designates A, T, C or G. Except as noted in Table 2, the use ofupper or lowercase letters to define the amino acids in a sequence isnot meant to convey a particular stereospecificity to the acids withinthe sequence.

Structure of Membrane-Permeant Peptide Covalent and CoordinationComplexes

The general structure of the present invention compounds comprises aunique combination of peptide components to produce a new class ofimaging and therapeutic conjugates that will enable interrogation of,and/or interaction with, the desired intracellular processes withinliving cells in the whole organism. This novel class of agents in itssimplest form comprises three components: 1) a cell membrane-permeantpeptide sequence made up of D-amino acids, L-amino acids or acombination of D- and L-amino acids; 2) a functional or non-functionallinker motif; and 3) a chelator moiety able to coordinate metals usefulin medical imaging and therapy (FIG. 1), or other cargo molecule such asa diagnostic substance or pharmaceutically active agent. The HIV-1 Tatbasic peptide sequence is an example of the prototypic cellmembrane-permeant component. The linker region can comprise amino acidresidues, or substituted or unsubstituted hydrocarbon chains useful forconnecting the Tat peptide and the metal chelator, for example, viapeptide bonds. The linker region can be designed to be non-functional orfunctional. “Non-functional” refers to non-reactive hydrocarbon chains,simple amino acid sequences, or other sequences that simply bindcovalently to the Tat peptide residues on one end and the cargo moleculeon the other end. A “functional linker” can comprise amino acid residuesthat confer biological properties useful for imaging, diagnostics,therapy, etc. Such a functionality could include peptide or proteinbinding motifs, protein kinase consensus sequences, protein phosphataseconsensus sequences, or protease-reactive or protease-specificsequences. Protease sequences are particularly useful as they willresult in amplification of an imaging, radiotherapeutic, diagnostic, ortherapeutic effect through enzymatic action on the conjugate complex,thereby increasing the intracellular concentration of a cleaved andsubsequently trapped metal-chelate or other cargo molecule.

Cell Membrane-Permeant Peptides

The cell membrane-permeant basic peptide component of the complexes ofthe present invention can comprise any amino acid sequence that confersthe desired intracellular translocation and targeting properties to thecovalent or coordination complexes. Preferably, these amino acidsequences are characterized by their ability to confer transmembranetranslocation and internalization of a complex construct whenadministered to the external surface of an intact cell, tissue or organ.The complex would be localized within cytoplasmic and/or nuclearcompartments as demonstrated by a variety of detection methods such as,for example, fluorescence microscopy, confocal microscopy, electronmicroscopy, autoradiography, or immunohistochemistry.

Cell membrane-permeant peptide sequences useful in practicing thepresent invention include, but are not limited to, RQARRNRRRRWRERQR-51(HIV-1 Rev protein basic motif; SEQ ID NO: 1); MPKTRRRPRRSQRKRPPTP-119(HTLV-1 Rex protein basic motif; SEQ ID NO: 2) (Kubota et al., Biochem.Biophys. Res. Comm., 162:963-970, 1989); the third helix of thehomeodomain of Antennapedia (Derossi, et al., J. Biol. Chem.271:18188-93, 1996) (43-RQILIWFQNRRMKWLL-58 (SEQ ID NO: 3)); a peptidederivable from the heavy chain variable region of an anti-DNA monoclonalantibody (Avrameas, et al., Proc. Natl. Acad. Sci. 95:5601-06, 1998)(VAYISRGGVSTYYSDTVKGRFTRQKYNKRA (SEQ ID NO: 4)); and the Herpes simplexvirus VP22 protein (Elliot and O'Hare, Cell, 88:223-33, 1997)(1-MTSRRSVKSGPREVPRDEYEDLYYTPSSGMASPDSPPDTSRRGALQTRSRQRGEVRFVQYDESDYALYGGSSSEDDEHPEVPRTRRPVSGAVLSGPGPARAPPPPAGSGGAGRTPTTAPRAPRTQRVATKAPAAPAAETTRGRKSAQPESAALPDAPASRAPTVQLWQMSRPRTDEDLNELLGITHRVTVCEGKNLLQRANELVNPDVVQDVDAATATRGRSAASRPTERPRAPARSASRPRRPVE-246 (SEQ ID NO: 5)). In apreferred embodiment, the basic peptide is derivable from the humanimmunodeficiency virus type 1 (HIV-1) Tat protein (Fawell et al., Proc.Natl. Acad. Sci., 91:664-68, 1994). In particular, the Tat peptide cancomprise any sequential residues of the Tat protein basic peptide motif37-72 (Vives et al., J. Biol. Chem., 272:16010-16017, 1997)(37-CFITKALGISYGRKKRRQRRRPPQGSQTHQVSLSKQ-72 (SEQ ID NO: 6).

Preferred examples of conjugate sequences with favorable cell uptake andU/W ratios include arginine-rich permeation peptide sequences based onthe Tat basic peptide, such as:

-   acetyl-RKKRRNRRR-AHA-εKGC-amide (SEQ ID NO: 33);-   acetyl-RKKRROrnRRR-AHA-εKGC-amide (SEQ ID NO: 34);-   acetyl-RKKRRERRR-AHA-εKGC-amide (SEQ ID NO: 35); and-   acetyl-RKKRRNorleuRRR-AHA-εKGC-amide (SEQ ID NO: 36) where Orn is    ornithine and Norleu is norleucine.

Other permeant peptides useful in the present invention includepoly-Arg, RRRRRRRRR (SEQ ID NO: 37); amphipathic polycationic peptide,RAARRAARR (SEQ ID NO: 38); and the viral permeation peptide,PLSSIFSRIGDP (SEQ ID NO: 39). As with all the inventive permeationpeptide sequences, such sequences may contain and shall be understood toencompass, the variable N-terminus, −4 substitutions and othermodifications taught herein.

The minimum number of amino acid residues can be in the range of fromabout three to about nine, preferably from about three to about five,and most preferably about four, i.e., the minimal requirement for onealpha helical turn. A preferred embodiment comprises Tat proteinresidues 48-57 (GRKKRRQRRR) (SEQ ID NO: 7). Residue number may beselected or modified to achieve a desired level of cellular uptake asthere is a correlation between decreased length of at least somepermeation peptides and decrease cellular uptake of the conjugate. Forexample, to generate the sequences identified as 13a,14a,15,16,17 ofTable 2, one additional amino acid was removed from the N-terminus ofthe longest Tat basic domain sequence (RKKRRQRRR) while all otheraspects of the peptide remained the same. From this data, a correlationbetween decreasing length and decreasing uptake of Tat basic domainpeptide was observed (FIG. 11). Similarly, there was an overall decreasein net cell uptake of the L-poly-Arg peptide as the length shortenedfrom poly-Arg₉ to poly-Arg₇ and of D-poly-Arg peptide as lengthshortened from poly-Arg₈ to poly-Arg₆. However, for the series 18-21(RAARRAARR), a putative amphipathic sequence with α-helical properties,there was relatively modest uptake and no change with decreasing length(FIG. 11).

In one preferred embodiment any of the aforementioned membrane peptidesmay contain at least one D-amino acid. In another preferred embodiment,a majority of the amino acid residues in any of the aforementionedpeptides can comprise D-amino acids. In yet another preferredembodiment, any of the aforementioned peptides are comprised entirely ofD-amino acids in forward sequence or inverse sequence (retro-inverse).In another preferred embodiment, all the amino acids of the membranepermeant peptide are D-amino acids whereas the remaining amino acids inthe conjugate, including the chelation moiety, may be either D or Lenantiomers. This aspect of the invention arises from the surprisingdiscovery that altering the chirality of the chelation moiety to allD-amino acids showed no significant difference in uptake compared to theL-peptides.

As used herein, the term “amino acid” is applicable not only to cellmembrane-permeant peptides, but also to linker moieties, coordinationligands, and other cargos, including pharmaceutical agents, i.e., allthe individual components of the present complexes. The term “aminoacid” is used in its broadest sense, and includes naturally occurringamino acids as well as non-naturally occurring amino acids, includingamino acid analogs and derivatives. The latter includes moleculescontaining an amino acid moiety. One skilled in the art will recognize,in view of this broad definition, that reference herein to an amino acidincludes, for example, naturally occurring proteogenic L-amino acids;D-amino acids; chemically modified amino acids such as amino acidanalogs and derivatives, including β-amino acids; naturally occurringnon-proteogenic amino acids such as norleucine, β-alanine, ornithine,etc.; and chemically synthesized compounds having properties known inthe art to be characteristic of amino acids. As used herein, the term“proteogenic” indicates that the amino acid can be incorporated into apeptide, polypeptide, or protein in a cell through a metabolic pathway.

The incorporation of non-natural amino acids, including syntheticnon-native amino acids, substituted amino acids, or one or more D-aminoacids into the peptides (or other components of the complexes) of thepresent invention (subsequently referred to herein as “D-peptides”) isadvantageous in a number of different ways. D-amino acid-containingpeptides exhibit increased stability in vitro or in vivo compared toL-amino acid-containing counterparts. Thus, the construction of peptidesincorporating D-amino acids can be particularly useful when greaterintracellular stability is desired or required. More specifically,D-peptides are resistant to endogenous peptidases and proteases, therebyproviding better oral transepithelial and transdermal delivery of linkeddrugs and conjugates, improved bioavailability of membrane-permeantcomplexes, and prolonged intravascular and interstitial lifetimes whensuch properties are desirable. The use of D-peptides can also enhancetransdermal and oral transepithelial delivery of linked drugs and othercargo molecules. As shown in Example 14, the use of D-amino acids in themembrane permeant peptide greatly increases the accumulation of linkeddrugs or other cargo molecules into cells. Additionally, D-peptidescannot be processed efficiently for major histocompatibility complexclass II-restricted presentation to T helper cells, and are thereforeless likely to induce humoral immune responses in the whole organism.Peptide conjugates can therefore be constructed using, for example,D-peptide membrane permeant sequences, L-peptide functional linkerdomains, and D-peptide chelation sequences. In this embodiment, only thefunctional L-peptide linker region would be able to interact with nativeenzymatic activities such as proteases, kinases, and phosphatases,thereby providing enhanced selectivity, prolonged biological half-life,and improved signal-to-noise ratio for selected imaging applications. Onthe other hand, when it is more desirable to allow the peptide to remainactive for only a short period of time, the use of L-amino acids in thepeptide can allow endogenous peptidases in a cell to digest the peptidein vivo, thereby limiting the cell's exposure to the membrane-permeantpeptide covalent and coordination complexes comprising the peptidesdisclosed herein. It will be apparent that it is possible to constructcomplexes in which different portions contain either D- or L-aminoacids. For example and without limitation, it is possible to construct acomplex in which a cell permeant peptide and a metal chelator comprisedof D-amino acids are connected by a functional linker comprised ofL-amino acids. Other such combinations will be readily apparent to thoseof ordinary skill in the art and are within the scope of the presentinvention.

In addition to using D-amino acids, those of ordinary skill in the artare aware that modifications in the amino acid sequence of a peptide,polypeptide, or protein can result in equivalent, or possibly improved,second generation peptides, etc., that display equivalent or superiorfunctional characteristics when compared to the original amino acidsequence. The present invention accordingly encompasses such modifiedamino acid sequences. Alterations can include amino acid insertions,deletions, substitutions, truncations, fusions, inversions, shuffling ofsubunit sequences, and the like, provided that the peptide sequencesproduced by such modifications have substantially the same functionalproperties as the naturally occurring counterpart sequences disclosedherein. Thus, for example, modified cell membrane-permeant peptidesshould possess substantially the same transmembrane translocation andinternalization properties as the naturally occurring counterpartsequence.

One factor that can be considered in making such changes is thehydropathic index of amino acids. The importance of the hydropathicamino acid index in conferring interactive biological function on aprotein has been discussed by Kyte and Doolittle (J. Mol. Biol., 157:105-132, 1982). It is accepted that the relative hydropathic characterof amino acids contributes to the secondary structure of the resultantprotein. This, in turn, affects the interaction of the protein withmolecules such as enzymes, substrates, receptors, DNA, antibodies,antigens, etc.

Based on its hydrophobicity and charge characteristics, each amino acidhas been assigned a hydropathic index as follows: isoleucine (+4.5);valine (+4.2); leucine (+3.8); phenylalanine (+2.8); cysteine/cystine(+2.5); methionine (+1.9); alanine (+1.8); glycine (−0.4); threonine(−0.7); serine (−0.8); tryptophan (−0.9); tyrosine (−1.3); proline(−1.6); histidine (−3.2); glutamate/glutamine/aspartate/asparagine(−3.5); lysine (−3.9); and arginine (−4.5).

As is known in the art, certain amino acids in a peptide or protein canbe substituted for other amino acids having a similar hydropathic indexor score and produce a resultant peptide or protein having similarbiological activity, i.e., which still retains biological functionality.In making such changes, it is preferable that amino acids havinghydropathic indices within ±2 are substituted for one another. Morepreferred substitutions are those wherein the amino acids havehydropathic indices within ±1. Most preferred substitutions are thosewherein the amino acids have hydropathic indices within ±0.5.

Like amino acids can also be substituted on the basis of hydrophilicity.U.S. Pat. No. 4,554,101 discloses that the greatest local averagehydrophilicity of a protein, as governed by the hydrophilicity of itsadjacent amino acids, correlates with a biological property of theprotein. The following hydrophilicity values have been assigned to aminoacids: arginine/lysine (+3.0); aspartate/glutamate (+3.0±1); serine(+0.3); asparagine/glutamine (+0.2); glycine (0); threonine (−0.4);proline (−0.5±1); alanine/histidine (−0.5); cysteine (−1.0); methionine(−1.3); valine (−1.5); leucine/isoleucine (−1.8); tyrosine (−2.3);phenylalanine (−2.5); and tryptophan (−3.4). Thus, one amino acid in apeptide, polypeptide, or protein can be substituted by another aminoacid having a similar hydrophilicity score and still produce a resultantprotein having similar biological activity, i.e., still retainingcorrect biological function. In making such changes, amino acids havinghydropathic indices within ±2 are preferably substituted for oneanother, those within ±1 are more preferred, and those within ±0.5 aremost preferred.

As outlined above, amino acid substitutions in the peptides of thepresent invention can be based on the relative similarity of the aminoacid side-chain substituents, for example, their hydrophobicity,hydrophilicity, charge, size, etc. Exemplary substitutions that takevarious of the foregoing characteristics into consideration in order toproduce conservative amino acid changes resulting in silent changeswithin the present peptides, etc., can be selected from other members ofthe class to which the naturally occurring amino acid belongs. Aminoacids can be divided into the following four groups: (1) acidic aminoacids; (2) basic amino acids; (3) neutral polar amino acids; and (4)neutral non-polar amino acids. Representative amino acids within thesevarious groups include, but are not limited to: (1) acidic (negativelycharged) amino acids such as aspartic acid and glutamic acid; (2) basic(positively charged) amino acids such as arginine, histidine, andlysine; (3) neutral polar amino acids such as glycine, serine,threonine, cysteine, cystine, tyrosine, asparagine, and glutamine; and(4) neutral non-polar amino acids such as alanine, leucine, isoleucine,valine, proline, phenylalanine, tryptophan, and methionine. It should benoted that changes which are not expected to be advantageous can also beuseful if these result in the production of functional sequences.

Additionally, substitutions may be made based on sequence specificeffects and the charge of particular amino acids. For example, it is ofparticular usefulness in the present invention to increase the cationiccharge of the permeation peptide used in the conjugate to enhancecellular uptake. One method of accomplishing this is the substitution ofone or more positively charged amino acids for one or more negativelycharged acids in the permeant peptide. For example, substitution of thepositively charged amino acid Orn for the naturally occurring negativelycharged amino acid at C-4 in the Tat basic peptide sequence increasesthe cellular uptake of a conjugate comprising such peptide (FIG. 12). Onthe other hand, substituting at the same position with the negativelycharged Glu, decreased cellular uptake.

The permeation peptide sequences of the present invention are effectiveregardless of N-terminus biotinylation or acetylation. Specifically, thepresence of biotin or acetyl groups on the N-terminus of the variouspermeation peptides did not significantly change their cell uptake asshown in Table 2. Thus, sequence identifications herein which includespecific N-terminus moieties should not be interpreted as requiring anyN-terminus or as limiting such sequences to such moieties.

Since small peptides can be easily produced by conventional solid phasesynthetic techniques, the present invention includes peptides, linkerregions, and cargo molecules such as those discussed herein, containingthe amino acid modifications discussed above, alone or in variouscombinations. To the extent that such modifications can be made whilesubstantially retaining the cell membrane permeant and targetingproperties of the peptide, and the biological function and specificityof the linker region and cargo moieties, they are included within thescope of the present invention. The utility of such modified peptides,linkers, and cargos can be determined without undue experimentation by,for example, the methods described in the examples below.

Linker Regions

Linker regions useful in linking the Tat or other cell membrane-permeantpeptides described herein and cargos such as drugs or diagnosticsubstances such as metal chelator moieties can comprise amino acidresidues or substituted or unsubstituted hydrocarbon chains. Usefullinker regions include natural and unnatural biopolymers. Examples ofnatural linkers include oligonucleotides and L-oligopeptides, whileexamples of unnatural linkers are D-oligopeptides, lipid oligomers,liposaccharide oligomers, peptide nucleic acid oligomers, polylactate,polyethylene glycol, cyclodextrin, polymethacrylate, gelatin, andoligourea (Schilsky, et al., Eds., Principles of Antineoplastic DrugDevelopment and Pharmacology, Marcel Dekker, Inc., New York, 1996, pp.741). The linker region can be designed to be functional ornon-functional.

“Non-functional” as applied to linker regions means any non-reactiveamino acid sequence, hydrocarbon chain, etc., that can bond covalentlyto Tat or other cell membrane-permeant peptide residues on one end and adrug or chelating ligand, for example, on the other end. As used herein,the term “non-reactive” refers to a linker that is biologically inertand biologically stable when a complex containing the linker iscontacted by cells or tissues. Upon characterization, the linker andconjugate can be shown to remain intact as the parent compound whenanalyzed by reverse phase HPLC or TLC. Non-functional linkers aredesirable in the design and synthesis of complexes useful, for example,in non-specific labeling of white blood cells for imaging infections, innon-specific labeling of tissues for perfusion imaging, and ininteraction with any intracellular receptor or other activity or site.Examples of non-functional linkers include, but are not limited to,amino hexanoic acid, glycine, alanine, or short peptide chains ofnonpolar amino acids such as di- or tri-glycine or tri-alanine.Hydrocarbon chain linkers can include both unsubstituted and substitutedalkyl, aryl, or macrocyclic R groups, as disclosed in U.S. Pat. No.5,403,574. R groups are found in the general formula —CR₃ where R can beidentical or different and includes the elements H, C, N, O, S, F, Cl,Br, and I. Representative examples include, but are not limited to,—CH₃, —CH₂CH₃, —CH(CH₃)₂, —C(CH₃)₃, —C(CH₃)₂, —OCH₃, —C(CH₃)₂, —COOCH₃,—C(CH₃)₂OCOCH₃, CONH₂, —C₆H₅, —CH₂(C₆H₄)OH, or any of their isomericforms. “Alkyl” is intended to mean any straight, branched, saturated,unsaturated or cyclic C₁₋₂₀ alkyl group. Typical C₁-C₂₀ alkyl groupsinclude, but are not limited to, methyl, ethyl, n-propyl, i-propyl,n-butyl, t-butyl, i-butyl, pentyl and hexyl groups. “Aryl” is intendedto mean any aromatic cyclic hydrocarbon based on a six-membered ring.Typical aryl groups include, but are not limited to, phenyl, naphthyl,benzyl, phenethyl, phenanthryl, and anthracyl groups. The term“macrocycle” refers to R groups containing at least one ring containingmore than seven carbon atoms. “Substituted” is intended to mean anyalkyl, aryl or macrocyclic groups in which at least one carbon atom iscovalently bonded to any functional groups comprising the atoms H, C, N,O, S, F, Cl, Br or I.

“Functional” as applied to linker regions means, for example, amino acidresidues, oligonucleotides, oligosaccharides, peptide nucleic acids, orsubstituted or unsubstituted hydrocarbon chains as discussed above thatconfer biological or physicochemical properties useful for the practiceof this invention when incorporated into the linker component. Suchproperties include, for example, utility in medical imaging,radiotherapy, diagnosis, and pharmacological treatment of disease statesby virtue of interaction of the functional linker region withintracellular components, which can be unique to, or highlycharacteristic of, cells in particular physiological or disease states.Such interaction can include, for example, binding or other reaction,for example cleavage, of the functional linker region due to interactionwith intracellular components. However this interaction occurs, suchinteraction results in selective retention of the cargo molecule withinparticular cells due to the presence of a particular intracellularcomponent(s) within such cells. The interaction of the functional linkerwith the intracellular component thereby confers target cell specificityto a peptide complex containing a particular functional linker moiety.Examples of functional linkers are peptide or protein binding motifs,protein kinase consensus sequences, protein phosphatase consensussequences, or protease-reactive or protease-specific sequences.Additional examples include recognition motifs of exo- andendo-peptidases, extracellular metalloproteases, lysosomal proteasessuch as the cathepsins (cathepsin B), HIV proteases, as well assecretases, transferases, hydrolases, isomerases, ligases,oxidoreductases, esterases, glycosidases, phospholipases, endonucleases,ribonucleases and β-lactamases.

Specific examples of useful consensus sequences and recognition motifsare: 14-3-3 protein binding motifs such as RSXSphosphoSXP (SEQ ID NO: 8)or RXY/FXphosphoSXP (SEQ ID NO: 9) (Yaffe et al., Cell, 91:961-971,1997). Preferred embodiments include the 14-3-3 protein binding motifsRLSHphosphoSLP (SEQ ID NO: 10), RLYHphosphoSLP (SEQ ID NO: 11) (Peng, etal., Science 277:1501-1505, 1997); and RLSHphosphoSLG (SEQ ID NO: 12).Protease-reactive or specific consensus sequences include, for example,those peptide sequences recognized by interleukin-1β converting enzyme(ICE) homologues, such as caspase-1, CPP32/Yama/apopain/caspase-3,NEDD2/Ich-1/caspase-2, TX/Ich-2/caspase-4,ICE-LAP3/MCH-3/CMH-1/caspase-7, ICE-LAP6/caspase-9, andFLICE/MACH/caspase-8 ((Nakagawara et al. Cancer Res., 57:4578-4584,1997) and references therein), including YEVDx (SEQ ID NO: 13) forCaspase-1, YDVADx (SEQ ID NO: 14) for Caspase-2, DEVDx (SEQ ID NO: 15)and DMQDx (SEQ ID NO: 16) for Caspase-3, LEVDx ((SEQ ID NO: 17) forCaspase-4, VEIDx (SEQ ID NO: 18) for Caspase-6, DEVDx (SEQ ID NO: 19)for Caspase-7, IETDx (SEQ ID NO: 20) for Caspase-8, and IEADx (SEQ IDNO: 21) for Caspase-10 (Villa, et al., Trends Biochem Sci 22:388-393,1997); SQVSQNY-PIVQNLQ (SEQ ID NO: 22) for the HIV p17-p24 A cleavagesite, and CTERQAN-FLGKIWP (SEQ ID NO: 23) for the HIV p7-p1 D cleavagesite (Ratner, et al., Nature 313:277-284, 1985; Welch, et al., Proc NatlAcad Sci USA 88:10792-10796, 1991); xR(R/K)x(S/T)x for Protein Kinase A,x(R/K)₂₋₃x(S/T)x for Protein Kinase G, X(R/K₁₋₃,x₀₋₂)(S/T)(X₀₋₂,R/K₁₋₃)xfor Protein Kinase C, xRxx(S/T)x for Calmodulin Kinase II, KRKQI(S/T)VR(SEQ ID NO: 24) for Phosphorylase b Kinase, TRDIYETDYYRK (SEQ ID NO: 25)for Insulin Receptor Kinase, and TAENAEYLRVAP (SEQ ID NO: 26) for EGFReceptor Kinase (Kemp and Pearson, Trends Biochem Sci 15:342-346, 1990;Kennelly and Krebs, J Biol Chem 266:15555-15558, 1991). Examples ofother useful non-peptide motifs include, for example, DNA recognitionsequences such as 3′-TCTTGTnnnACAAGA-5′ (SEQ ID NO: 27) for theglucocorticoid hormone response element, 3′-TCCAGTnnnACTGGA-5′ (SEQ IDNO: 28) for the estrogen receptor response element, and3′-TCCAGTACTGGA-5′ (SEQ ID NO: 29) for the thyroid hormone responseelement (Fuller, FASEB J 5:3092-3099, 1991). Additional sequences knownto those skilled in the art and available by reference to publicdatabases can be incorporated into the linker moieties of the presentcomplexes. Well known protein, DNA, and RNA databases available toinvestigators working in the art of biomedical and pharmaceuticalsciences include those linked to the U.S. National Institutes of HealthWeb Site, such as: http://molbio.info.nih.gov/molbio/, all hereinincorporated by reference. A biomolecule or fragment thereof containinga putative recognition motif can be identified by sequence comparison ofthe primary structure with a primary consensus sequence or individualsequence of a protein or biomolecule in the databases using routinecomputerized sequence scanning methods such as, for example, BLAST.

When incorporated into the intact Tat or other peptide complexes of thepresent invention, such sequence motifs will be acted on solely orselectively in those cells containing the appropriate intracellularsequence-specific or sequence-reactive protein, which will alter theintracellular/subcellular distribution and retention of the cargomolecule, e.g., a drug or metal chelate. For example, protease sequencesare particularly useful as they result in enzymatic amplification of animaging or radiotherapeutic effect through enzymatic action on theconjugate complex, thereby cleaving and subsequently trappingmetal-chelates within intracellular compartments, leading to an increasein the concentration of the metal-complex fragment.

To further illustrate this principle, if the intracellular target to bedetected is a specific protease activity of the caspase family, thenwhen a coordination complex of the present invention comprising thecomponents (Tat peptide)-(caspase-3 motif linker)-(chelate{metal})translocates into a cell containing caspase-3, the enzyme will cleavethe complex in the linker region, thereby releasing the metal-chelatewithin the cell interior, which can then be monitored by conventionaltechniques. Of course, such target specificity could also beaccomplished by the use of a caspase reactive diagnostic substance aswell.

Cells or tissues having other biological, biochemical, or physiologicalactivities can also be detected when the appropriate functional linkeris incorporated into the covalent or coordination complex. For example,a hexose sequence recognized by β-galactosidase can be synthesized intothe linker region of the invention compounds, e.g., as (Tatpeptide)-(D-galactose-D-glucose)-(chelate{metal}). Then, uponadministration to cells transduced with a marker gene that encodesβ-galactosidase, for example in gene therapy, only those cells whichexpress β-galactosidase will cleave and retain the chelate-metal complexfor subsequent detection by external imaging devices.

Metal-chelate moieties can be synthesized to possess net charge, forexample, by substitution of K for G on the εKGC chelation peptide asillustrated in Example 1. This is useful for in vivo applications in awhole animal. Because non-targeted or unreacted Tat peptide conjugatesare capable of bidirectionally translocating across membranes, as theextracellular concentration of a Tat peptide conjugate declines, theintracellular intact Tat peptide conjugate will translocate outwardlyand be cleared from the animal via the bloodstream. However, whereprotease cleavage acts on the peptide, the Tat fragment is separatedfrom the chelate fragment, which further generates a positive charge atthe amino-terminus of the cleaved chelate fragment. Thus, the overallcharge of the released peptide chelate complex will be polycationic.This cluster of charge combined with the lack of an attached Tatpermeation sequence will render the cleaved chelate fragment impermeantto the cell membrane, in effect trapping the chelate fragment within thecell both in vivo and in vitro. In cells lacking the targeted proteaseactivity, the intact Tat peptide-chelate complex translocates outwardlyinto the extracellular spaces as the extracellular concentration of theTat peptide decreases. This clearance has been found to occursurprisingly rapidly in vivo. The present invention exploits this highclearance rate to provide high target-to-background ratios for imaging,diagnostics, and therapeutic delivery of metal chelates and drugconjugates to specific cells, tissues and organs.

In cases where the metal-chelate comprises a radioactive metal, thenexternal imaging devices such as scintigraphic gamma cameras or SPECTwill only detect high radioactivity within cells, tissues or organscontaining the desired biological activity. In contrast, if themetal-chelate comprises a ligand complexed with a relaxivity metal, suchas Gd-DTPA, then the resulting enhanced T1 relaxivity would bedetectable within cells and tissues of living patients using appropriateT1-weighted pulse sequences generated by clinical magnetic resonanceimaging (MRI) devices. Those skilled in the art can readily operate theappropriate MRI device to detect proton relaxivity changes in bodilywater induced by relaxivity complexes known as MR contrast agents (Starkand Bradley, Magnetic Resonance Imaging, C. V. Mosby Co., St. Louis,1988, pp. 1516). Thus, the present invention overcomes a limitationpresent in existing methods, which do not provide for the intracellulardeposition of peptide chelate-metal complexes for targeted medicalimaging with SPECT/PET and radiotherapeutic applications, nor allow theinterrogation of changes in intracellular proton relaxivity with MRIdevices. In contrast, the present invention provides for theintracellular delivery and targeted retention of desired metalcomplexes.

Various chelation peptides may be used in the present invention toensure effective chelation, to enhance cell uptake of the conjugate andto meet other structural or functional goals of a particular conjugationstrategy. For example, the Lys-Gly-Cys utilized in most of the exemplarconjugates was selected in light of its ability to efficiently chelate^(99m)Tc. Using a His-Gly chelation peptide to chelate ^(99m)Tc(CO)₃showed a significant increase in uptake of the conjugate. The His-Glypeptide would also allow for radiolabelling of the N-terminus andfurther conjugation at the C-terminus via an additional Cys amino acid.Using a Gly-Lys chelation peptide along with orthogonal conjugation ofthe chelation cargo to the e-amine of the Lys results in significantreduction in conjugate uptake but allowed double or triple labeling ofpeptides.

Other variations are possible wherein the Tat or otherpeptide-linker-metal complexes contain a functional linker and aresufficiently stable to be delivered to the desired cells andtranslocated into the cell interior, where they will be acted upon bythe targeted intracellular biochemical activity and the retainedmetal-chelates detected with imaging devices as above.

In addition to radioactive and non-radioactive metals, pharmacologicallyactive substances, prodrugs, cytotoxic substances, and diagnosticsubstances such as fluorochromes, dyes, enzyme substrates, etc., can becoupled to the linkers of the present membrane-permeant peptidecomplexes. A wide variety of drugs are suitable for use with the presentinvention, and include, for example, conventional chemotherapeutics,such as vinblastine, doxorubicin, bleomycin, methotrexate,5-fluorouricil, 6-thioguanine, cytarabine, cyclophosphamide, taxol,taxotere, cis-platin, adriamycin, mitomycin, and vincristine as well asother conventional chemotherapeutics as described in Cancer: Principlesand Practice of Oncology, 5th Ed., V. T. Devita, S. Hellman, S. A.Rosenberg, J. B. Lippincott, Co., Phila, 1997, pp. 3125. Also suitablefor use in the present invention are experimental drugs, such as UCN-01,acivicin, 9-aminocamptothecin, azacitidine, bromodeoxyuridine,bryostatin, carboplatin, dideoxyinosine, echinomycin, fazarabine,hepsulfam, homoharringtonine, iododeoxyuridine, leucovorin, merbarone,misonidazole, pentostatin, semustine, suramine, mephthalamidine,teroxirone, triciribine phosphate and trimetrexate as well as others aslisted in NCI Investigational Drugs, Pharmaceutical Data 1994, NIHPublications No. 94-2141, revised January 1994.

In addition, the radioactive and non-radioactive metals,pharmacologically active substances, prodrugs, cytotoxic substances, anddiagnostic substances used herein may themselves provide target cellspecificity. Such specificity may be particularly effective where suchsubstances are used in a conjugate with a non-functional linker of thepresent invention.

Other useful drugs include anti-inflammatories such as Celebrex,indomethacin, flurbiprofen, ketoprofen, ibuprofen and phenylbutazone;antibiotics such as beta-lactams, aminoglycosides, macrolides,tetracyclines, pryridonecarboxylic acids and phosphomycin; amino acidssuch as ascorbic acid and N-acetyltryptophan; antifungal agents;prostaglandins; vitamins; steroids; and antiviral agents such as AZT,DDI, acyclovir, gancyclovir, idoxuridine, amantadine and vidarabine.

Pharmacologically active substances that can be conjugated to thecomplexes of the present invention include, but are not limited to,enzymes such as transferases, hydrolyses, isomerases, proteases,ligases, kinases, and oxidoreductases such as esterases, phosphatases,glycosidases, and peptidases; enzyme inhibitors such as leupeptin,chymostatin and pepstatin; growth factors; and transcription factors ordomains derived from each.

In addition, the present invention can be used to deliver fluorochromesand vital dyes into cells. Examples of such fluorochromes and vital dyesare well known to those skilled in the art and include, for example,fluorescein, rhodamine, coumarin, indocyanine Cy 5.5, NN382, Texas red,DAPI, EDANS, DABCYL and ethidium bromide.

The delivery of drug and pharmacologically active compounds into thecell interior can be enhanced by direct conjugation to the Tat or othermembrane-permeant peptides of the present invention. The coupling ofsuch compounds to a functional linker placed between a D-amino acidcontaining cell membrane-permeant peptide and the active agent, therebyenabling enhanced, functionally selective, intracellular trapping of thedrug or drug conjugate, is new. A drug or prodrug conjugate designed asdescribed herein would enable selective delivery (and retention) ofbioactive agents and therapeutic or biologic enhancers useful in therapyincluding, but not limited to, granulocyte-stimulating factors,platelet-stimulating factors, erythrocyte-stimulating factors,macrophage-colony stimulating factors, interleukins, tumor necrosisfactors, interferons, other cytokines, monoclonal antibodies, immuneadjuvants and gene therapy vectors (Devita, et al., Biologic Therapy ofCancer, 2nd Ed., J. B. Lippincott, Co., Phila, 1995, pp. 919), and drugsinto the cell interior in a manner analogous to the selective trappingof metal chelates as described above. Linker functionality can includeany motif that can be acted on by a specific intracellular agent, suchas the enzymes discussed above, or ribozymes, for example. Examples ofsuch linker functionalities include low molecular weight peptide orprotein binding motifs, protein kinase consensus sequences, proteinphosphatase consensus sequences, or protease-specific sequences. Asexplained previously, protease-reactive or protease-specific sequencesare particularly useful in that amplification of the therapeutic effectwould occur through enzymatic action on the linker region of the drug orprodrug conjugate, thereby releasing the pharmacological agent in thecell cytosol, and increasing the intracellular retention andconcentration of the agent.

Pharmacologically active substances, cytotoxic substances, diagnosticsubstances, etc., can be coupled to the appropriate cellmembrane-permeant peptide-linker conjugate through either the amino- orcarboxy-terminus of the linker region in a manner analogous to thatdescribed in Example 1. For example, drug conjugates wherein thecarboxy-terminus of the peptide linker is coupled to a bioactivesubstance can be prepared by the use of an active ester of the desiredbioactive substance in the presence of a dehydrating agent. Examples ofactive esters that can be used in the practice of the present inventioninclude the hemi-succinate esters of N-hydroxysuccinimide,sulfo-N-hydroxy-succinimide, hydroxybenzotriazole, and p-nitrophenol.Dehydration agents include dicyclohexylcarbodiimide (DCC),1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (ECD), and1-(3-dimethylaminopropyl)-3-ethylcarbodiimide methiodide (EDCI). The useof ECD to form conjugates is disclosed in U.S. Pat. No. 4,526,714, thedisclosure of which is fully incorporated by reference herein. Otherexamples of coupling reagents include glutathione,3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT), oniumsalt-based coupling reagents, polyoxyethylene-based heterobifunctionalcross-linking reagents, and other reagents that facilitate the couplingof organic drugs and peptides to various ligands (Haitao, et al., OrganLett 1:91-94, 1999; Albericio, et al., J Organic Chemistry 63:9678-9683,1998; Arpicco, et al., Bioconjugate Chem 8:327-337, 1997; Frisch, etal., Bioconjugate Chem 7:180-186, 1996; Deguchi, et al., BioconjugateChem 10:32-37, 1998; Beyer, et al., J Med Chem 41: 2701-2708, 1998;Dirven, et al., Chem Res Toxicol 9:351-360, 1996; Drouillat, et al., JPharm Sci 87:25-30, 1998; Trimble, et al., Bioconjugate Chem 8:416-423,1997). Chemicals, reagents and techniques useful in drug cross-linkingand peptide conjugation are disclosed in general texts well known tothose skilled in the art (Dawson, et al., (Eds.), Data for BiochemicalResearch, 3rd Ed., Oxford University Press, Oxford, UK, 1986, pp. 580;King, (Ed.), Medicinal Chemistry: Principles and Practice, Royal Societyof Chemistry, Cambridge, UK, 1994, pp. 313; Shan and Wong, (Eds.),Chemistry of Protein Conjugation and Cross-Linking, CRC Press, BocaRaton, 1991, pp. 328). Additional chemical coupling agents are describedin U.S. Pat. No. 5,747,641, hereby incorporated by reference in itsentirety.

Conjugated Chelate Ligands and Drugs

The present invention also encompasses the use of chelation ligands toform coordinate bonds with desired metals. The desired chelation ligandsare attached to the peptide conjugate where they bind radionuclides anddesired non-radioactive metals in a highly efficient and stable manner.When the metal is a radionuclide, this allows the reporting of thespatial location of the conjugate with external imaging devices such asSPECT and PET detectors following administration of the conjugate to ananimal. As disclosed above, preferred embodiments of the presentinvention permit the chelation moiety to be concentrated within cellularand tissue compartments in proportion to specific enzymatic or proteinactivities present in the cells therein. In other preferred embodiments,where the metal is a selected therapeutic radionuclide, the presentinvention allows the chelation moiety to be concentrated within targetcellular and tissue compartments in proportion to a specific enzymaticor protein activity to deposit radiation selectively within the targetcell or tissue. In another preferred embodiment, when the metal is arelaxivity metal, the chelation moiety permits magnetic resonanceimaging of the cell or tissue. Alternatively, when the functional linkerregion of the permeant peptide construct is conjugated to a drug, thedrug will be selectively deposited within the target cell or tissue bymethods of this invention.

Suitable chelation ligands are well known to those skilled in the artand include, but are not limited to, diethylenetriaminepentaacetic acid(DTPA), ethylenediaminetetraacetic acid (EDTA),tetraazacyclododecanetetraacetic acid (DOTA), and other chelators thatincorporate electron donating atoms such as O, S, P or N as Lewis basesto bind the metal (Engelstad and Wolf, “Contrast Agents”, in MagneticResonance Imaging, Stark and Bradley, Mosby, St. Louis, 1988, pp.161-181). The present complexes can also employ chelating ligands suchas, but not restricted to, those containing N₂S₂, N₃S, N₂SO and NS₃)moieties (Meegalla et al., J. Med. Chem., 40:9-17, 1997). Specificexamples (as shown below) wherein these chelation moieties areincorporated into specific sequences of peptide residues, such asε-amine modified Lys-Gly-Cys tags, are especially convenient forsynthesizing the desired chelation groups directly into peptide-basedsequences. Preferred chelation ligands are peptides or modified peptideswhich enable the chelation moiety to be incorporated into the peptideconstruct directly by solid phase synthesis by use of appropriatelyblocked peptide precursors compatible with commercial peptidesynthesizers. Examples of this preferred embodiment are illustratedbelow in more detail. Alternatively, other preferred chelation ligandscan be chemically coupled to the peptide conjugate by use of one or moreof the linker reagents described above. Other preferred embodiments ofthe invention encompass the conjugation of drugs or therapeutics,including therapeutic peptides, to the functionalized linker regionattached to the permeant peptide. In one embodiment, the chelationcomplexes of the present invention comprise a peptide-based chelatorwherein the coordination sites of the chelator are filled with a metaluseful in imaging or radiotherapy.

Radioactive and Non-Radioactive Metals

Useful metals for chelation into the complexes of the present inventioninclude radionuclides having decay properties that are amenable for useas a diagnostic tracer or for deposition of medically useful radiationwithin cells or tissues. The present invention consequently encompassesthe use of conjugated coordination complexes of a ligand with aradioactive metal (radionuclide). The radioactive nuclide can, forexample, be selected from the group consisting of radioactive isotopesof Tc, Ru, In, Ga, Co, Pt, Fe, Os, Ir, W, Re, Cr, Mo, Mn, Ni, Rh, Pd,Nb, Cu and Ta, for example, Tc-99m, Tc-99, In-111, Ga-67, Ga-68, Cu-64,Ru-97, Cr-51, Co-57, Re-188, and Re-186. Such complexes can be used formedical imaging and specifically for SPECT or PET imaging, as providedherein. Technetium-99m (Tc-99m; t½=6 hours; 140 keV emission photon) isthe most commonly used radionuclide in diagnostic nuclear medicine(Jurisson et al., Chem. Rev., 93:1137-156, 1993). It can be readilyproduced by molybdenum-99/technetium-99m generators available inclinical nuclear medicine radiopharmacy laboratories, and has favorableemission characteristics that enable ready detection with clinical gammacameras. While the complexes of the present invention preferably containTc-99m and the closely related rhenium isotopes (Re-186 and Re-188),other radionuclides and metals, in addition to those already listed,useful for imaging and radiotherapy such as I-123, I-125, I-130, I-131,I-133, Sc-47, As-72, Se-72, Y-90, Y-88, Pd-100, Rh-100m, Sb-119, Ba-128,Hg-197, At-211, Bi-212, Pd-212, Pd-109, Cu-67, Br-75, Br-76, Br-77,C-11, N-13, O-15, F-18, Pb-203, Pb-212, Bi-212, Cu-64, Ru-97, Rh-105,Au-198, and Ag-199 are also encompassed within the scope of thisinvention. Moreover, the general availability of supplies ofpertechnetate from a variety of vendors makes it convenient to use kitsfor preparation of various peptide complexes of Tc-99m. Labeling of thepeptide conjugates of the present invention with radioactive metals canbe readily performed. In preferred embodiments of this invention, thepeptide conjugate is radiolabeled with ^(99m)Tc using standard reducingagents with or without transmetallation reactions (Grummon, et al.,Inorg Chem 34:1764-1772, 1995; Lister-James, et al., J Nucl Med37:775-781, 1997; Meegalla, et al., J Med Chem 40:9-17, 1997).

Useful metals also include isotopes of those metals possessingparamagnetism which produce water relaxation properties useful forgenerating images with magnetic resonance imaging (MRI) devices.Suitable relaxivity metals include, but are not limited to, Mn, Cr, Fe,Gd, Eu, Dy, Ho, Cu, Co, Ni, Sm, Tb, Er, Tm, and Yb. Appropriatechelation ligands to coordinate MR relaxivity metals can be readilyincorporated into the peptide complexes of this invention by the methodspreviously described for radionuclides. Such chelation ligands caninclude, but are not limited to, DTPA, EDTA, DOTA, TETA, EHPG, HBED,ENBPI, ENBPA, and other macrocycles known to those skilled in the art(Stark and Bradley, Magnetic Resonance Imaging, C. V. Mosby Co., StLouis, 1988, pp 1516).

The peptide metal coordination complexes of the present invention can bereadily prepared by methods known in the art. For example, a Tat orother cell membrane-permeant peptide conjugated to a linker and a metalchelating moiety can be admixed with a salt of the radioactive metal inthe presence of a suitable reducing agent, if required, in aqueous mediaat temperatures from room temperature to reflux temperature, and theend-product coordination complex can be obtained and isolated in highyield at both macro (carrier added, e.g., Tc-99) concentrations and attracer (no carrier added, e.g., Tc-99m) concentrations (typically lessthan 10⁻⁶ molar). It is well established that when (Tc-99m)pertechnetate (TcO₄ ⁻) is reduced by a reducing agent, such as stannouschloride, in the presence of chelating ligands such as, but notrestricted to, those containing N₂S₂, N₂SO, N₃S and NS₃ moieties,complexes of (TcO)N₂S₂, (TcO)N₂SO, (TcO)N₃S and (TcO)NS₃ are formed(Meegalla et al. J. Med. Chem., 40:9-17, 1997). Another preferred methodfor radio labeling the peptide involves the use of glucoheptonatetogether with a reducing agent such as stannous chloride to label thechelation moiety on the peptide (Lister-James, et al., J Nucl Med37:775-781, 1997; Meegalla, et al., J Med Chem 40:9-17, 1997). Anotherpreferred labeling method involves one-step labeling of His-taggedpeptides with Tc(I)-carbonyl complexes (Waibel, et al., NatureBiotechnology, 17:897-901, 1999). Such Tc-99m labeling and chelatingmoieties can be incorporated into potential receptor-selective imagingagents (Horn and Katzenellenbogen, Nucl. Med. Biol., 24:485-498, 1997).The incorporation of such moieties, specifically those that chelateradioactive metals or other metals of interest for imaging (e.g.,magnetic resonance relaxivity metals) or radiotherapy, into the Tat orother peptide motif via the use of a functional linker, thereby enablingselective intracellular delivery and retention of the metal coordinationcomplex, is new. Non-radioactive metals useful for MR imaging can beincorporated into an appropriate chelator useful for binding relaxivitymetals which in turn has been conjugated onto the peptide linkerconstruct as described above. A preferred embodiment of this inventionis the coupling of DOTA to the peptide conjugate using methodsreferenced above and using Gd as the MR relaxivity metal. Gd can bechelated into the DOTA moiety by reaction of chloride salts of Gd, suchas GdCl₃, with the peptide chelate conjugate under mildly acidicconditions (pH 5-6) using standard techniques (Stark and Bradley,Magnetic Resonance Imaging, C. V. Mosby Co., St. Louis, 1988, pp. 1516;Wen-hong, et al., J Am Chem Soc 121:1413-1414, 1999).

Other Applications

The present complexes can also be used in fluorescence resonance energytransfer (FRET) to study intracellular processes. When used with theFRET methodology, the functional linker is placed between thefluorescent energy donor and acceptor. Examples of suitable pairs offluorescent energy donor and acceptors, as well as methods for usingFRET, are well known in the art and are described, for example, inUbarretxena-Belandia et al., Biochemistry, 38:7398-7405, 1999; Blomberget al., Clin. Chem., 45:855-861, 1999; and Jamieson et al., J Biol.Chem. 274:12346-12354, 1999. Near infrared fluorescent (NIRF) probes mayalso be appended on each side of the linker such that when the linker isintact, the probes are autoquenched and, when the linker is specificallycleaved, the NIRF probes fluoresce (Tyagi et al., Nature Biotech.,14:303-308, 1996).

In addition to providing compositions and methods for medical imaging,other diagnostic methods, and drug delivery, the present invention alsoprovides methods for evaluating intracellular processes in living cellsin vivo and in tissues in vitro. Examples of such processes includeprotein-protein binding, protein kinase activities, protein phosphataseactivities, or protease activities. Additional examples include theactivities of exo- and endo-peptidases, extracellular metalloproteases,lysosomal proteases such as the cathepsins (cathepsin B), as well as α-,β-, and γ-secretases, transferases, hydrolases, isomerases, ligases,oxidoreductases, esterases, glycosidases, phospholipases, endonucleases,ribonucleases and β-lactamases as they relate to the various diseasestates associated with loss of function or gain of function for each.These methods are performed by administering agents that aretranslocated across the plasma membrane into cells and which aredetectable in living cells despite the presence of biological tissueintervening between the detection device and the cells in their in situlocation. Thus, cells in the living body or in a tissue mass aredetectable in situ.

In accordance with the present invention, living cells can be imaged.Complexes of this invention useful in generating images are administeredto a patient, or to cells or a tissue specimen. Imaging proceduresinclude, but are not limited to, magnetic resonance imaging (MRI),superconducting quantum interference device (SQUID), near infraredimaging, optical fluorescence imaging, positron emission tomography(PET), and, in highly preferred embodiments, imaging is by planarscintigraphy or single photon emission computed tomography (SPECT).

These methods are also applicable to rapid and simple assays ofintracellular biochemical reactions in vitro and, more importantly, asassays in instances in which presently available assay methods areimpractical or impossible, such as in vivo and in situ. For example, inexcised tissues, intracellular functions include biochemical activitiessuch as protein-protein binding, protein kinase activities, proteinphosphatase activities, and protease activities. Additional examplesinclude the activities of exo- and endo-peptidases, extracellularmetalloproteases, lysosomal proteases such as the cathepsins (cathepsinB), as well as that of α-, β-, and γ-secretases, transferases,hydrolases, isomerases, ligases, oxidoreductases, esterases,glycosidases, phospholipases, endonucleases, ribonucleases andβ-lactamases, which can be detected without the need for tissuedispersion and growth that change the in vivo phenotype. These methodsare especially valuable for in vivo assays whereby intracellularbiological activities are detected without the need for traumaticsurgery.

By the use of the present methods, intracellular functions can bedetected in patients without the need for surgery. Accordingly, thepresent invention encompasses compounds and methods for detectingintracellular biochemical activities in living, whole animals, tissues,or cells by administering complexes of this invention which translocateinto cells, and which are detectable in living cells at distancesremoved from the cells by the presence of intervening tissue. Examplesof tissues to which the methods of the present invention can be appliedinclude, for example, cancer cells, in particular, central nervoussystem tumors, breast cancer, liver cancer, lung, head and neck cancer,lymphomas, leukemias, multiple myeloma, bladder cancer, ovarian cancer,prostate cancer, renal tumors, sarcomas, colon and othergastrointestinal cancers, metastases, and melanomas. More specifically,the present invention can be applied to cancers such as sarcomas andcarcinomas, e.g., fibrosarcoma, myxosarcoma, liposarcoma,chondrosarcoma, osteogenic sarcoma, chordoma, angiosarcoma,endotheliosarcoma, lymphangiosarcoma, lymphangioendotheliosarcoma,synovioma, mesothelioma, Ewing's tumor, leiomyosarcoma,rhabdomyosarcoma, colon carcinoma, pancreatic cancer, breast cancer,ovarian cancer, prostate cancer, squamous cell carcinoma, basal cellcarcinoma, adenocarcinoma, sweat gland carcinoma, sebaceous glandcarcinoma, papillary carcinoma, papillary adenocarcinomas,cystadenocarcinoma, medullary carcinoma, bronchogenic carcinoma, renalcell carcinoma, hepatoma, bile duct carcinoma, choriocarcinoma,seminoma, embryonal carcinoma, Wilms' tumor, cervical cancer, testiculartumor, lung carcinoma, small cell lung carcinoma, bladder carcinoma,epithelial carcinoma, glioma, astrocytoma, medulloblastoma,craniopharyngioma, ependymoma, pinealoma, hemangioblastoma, acousticneuroma, oligodendroglioma, meningioma, melanoma, neuroblastoma,retinoblastoma; leukemias, e.g., acute lymphocytic leukemia and acutemyelocytic leukemia (myeloblastic, promyelocytic, myelomonocytic,monocytic and erythroleukemia); chronic leukemia (chronic myelocytic(granulocytic) leukemia and chronic lymphocytic leukemia); andpolycythemia vera, lymphoma (Hodgkin's disease and non-Hodgkin'sdisease), multiple myeloma, Waldenstrom's macroglobulinemia, and heavychain disease. The present invention can also be used to detect thepresence of enzymes associated with diseases, conditions or disorders.Examples of diseases, conditions or disorders to which the presentinvention can be applied include, but are not limited to infection,inflammation, neurodegenerative diseases such as Alzheimer's disease andParkinson's disease, ALS, hypoxia, autoimmune diseases, immunedeficiencies, cardiovascular insults such as infraction and stroke, andconnective tissue disorders such as rheumatoid arthritis, lupis anddermatomyositis, and other specific dysfunctions of organs. Enzyme(s)associated with particular diseases, conditions, or disorders are wellknown to those skilled in the art and can be found in standard medicalreferences, for example, Stedman's Medical Dictionary, 26th Edition,Williams & Wilkins, 1995, and Harrison's Principles of InternalMedicine, 14th Edition, McGraw-Hill, 1998. The present inventiontherefore encompasses peptide conjugate metal coordination complexes(and other diagnostically useful complexes) and methods of detectingsuch complexes or their reaction products in living, whole animals,tissues, or cells by administering the present imaging complexes,especially a scintigraphic or magnetic resonance imaging complex, whichtranslocates into the interior of living cells.

Kits

The present invention also provides kits comprising a quantity of areducing agent for reducing a preselected radionuclide, as described,for example, by Jones et al., U.S. Pat. No. 4,452,774. Such kits cancontain a predetermined quantity of a Tat or other cell-permeant peptideconjugate and a predetermined quantity of a reducing agent capable ofreducing a predetermined quantity of a preselected radionuclide. Suchkits can contain a predetermined quantity of glucoheptonate. The peptideconjugate and reducing agent can be lyophilized to facilitate storagestability. The conjugate and reducing agent can be contained in asealed, sterilized container. Instructions for carrying out thenecessary reactions, as well as a reaction buffer solution(s), can alsobe included in the kit.

In one embodiment, the present invention provides a kit for use inpreparing cell membrane-permeant coordination complexes from a supply ofTc-99m such as pertechnetate solution in isotonic saline available inclinical nuclear medicine laboratories, including the desired quantityof a selected Tat or other peptide conjugate to react with a selectedquantity of pertechnetate, and a reducing agent such as sodiumdithionite or stannous chloride in an amount sufficient to reduce theselected quantity of pertechnetate to form the desired peptide metalcomplex. In a preferred embodiment, the kit includes a desired quantityof a selected peptide conjugate to react with a selected quantity ofreduced technetium supplied in the kit in the form ofTc-99m-glucoheptonate, itself produced from a stannous glucoheptonatecommercial kit (Dupont Pharma), and a reducing agent such as sodiumdithionite or stannous chloride in an amount sufficient to assure thatthe selected quantity of reduced technetium produces the desired peptidemetal complex.

Pharmaceutically Acceptable Salts of Peptide Complexes

Like amino acids, peptides and proteins are ampholytes, i.e., they actas both acids and bases by virtue of the presence of variouselectron-donor and acceptor moieties within the molecule. The peptidecomplexes of the present invention can therefore be used in the freeacid/base form, in the form of pharmaceutically acceptable salts, ormixtures thereof, as is known in the art. Such salts can be formed, forexample, with organic anions, organic cations, halides, alkaline metals,etc.

The term “pharmaceutically acceptable salts” embraces salts commonlyused to form alkali metal salts and addition salts of free acids or freebases. The nature of the salt is not critical, provided that it ispharmaceutically acceptable. Suitable pharmaceutically acceptable baseaddition salts of the present peptide complexes include metallic saltsand organic salts.

Preferred metallic salts include, but are not limited to, appropriatealkali metal (group Ia) salts, alkaline earth metal (group IIa) salts,and other physiologically acceptable metals. Such salts can be prepared,for example, from aluminum, calcium, lithium, magnesium, potassium,sodium, and zinc.

Organic salts can be prepared from tertiary amines and quaternaryammonium salts, including in part, tromethamine, diethylamine,N,N′-dibenzyl-ethylenediamine, chloroprocaine, choline, diethanolamine,ethylenediamine, meglumine (N-methyl-glucamine), and procaine.

Such salts can also be derived from inorganic or organic acids. Thesesalts include but are not limited to the following: acetate, adipate,alginate, citrate, aspartate, benzoate, benzenesulfonate, bisulfate,butyrate, camphorate, camphorsulfonate, digluconate,cyclopentanepropionate, dodecylsulfate, ethanesulfonate,glucoheptanoate, glycerophosphate, hemisulfate, heptanoate, hexanoate,fumarate, hydrochloride, hydrobromide, hydroiodide,2-hydroxy-ethanesulfonate, lactate, maleate, methanesulfonate,nicotinate, 2-naphthalenesulfonate, oxalate, palmoate, pectinate,persulfate, 3-phenylpropionate, picrate, pivalate, propionate,succinate, tartrate, thiocyanate, tosylate, mesylate, and undecanoate.

The basic nitrogen-containing groups can be quaternized with agents suchas lower alkyl halides, such as methyl, ethyl, propyl, and butylchloride, bromides, and iodides; dialkyl sulfates such as dimethyl,diethyl, dibuytl, and diamyl sulfates; long chain halides such as decyl,lauryl, myristyl, and stearyl chlorides, bromides, and iodides; aralkylhalides such as benzyl and phenethyl bromides, and others.

All of these salts can be prepared by conventional means from thecorresponding peptide complex disclosed herein by reacting theappropriate acid or base therewith. Water- or oil-soluble or dispersibleproducts are thereby obtained as desired.

Formulations/Pharmaceutical Compositions

The compounds of the present invention can be formulated aspharmaceutical compositions. Such compositions can be administeredorally, parenterally, by inhalation spray, rectally, intradermally,transdermally, or topically in dosage unit formulations containingconventional nontoxic pharmaceutically acceptable carriers, adjuvants,and vehicles as desired. Topical administration may also involve the useof transdermal administration such as transdermal patches oriontophoresis devices. The term parenteral as used herein includessubcutaneous, intravenous, intramuscular, or intrastemal injection, orinfusion techniques. Formulation of drugs is discussed in, for example,Hoover, John E., Remington's Pharmaceutical Sciences, Mack PublishingCo., Easton, Pa. (1975), and Liberman, H. A. and Lachman, L., Eds.,Pharmaceutical Dosage Forms, Marcel Decker, New York, N.Y. (1980).

Injectable preparations, for example, sterile injectable aqueous oroleaginous suspensions, can be formulated according to the known artusing suitable dispersing or wetting agents and suspending agents. Thesterile injectable preparation may also be a sterile injectable solutionor suspension in a nontoxic parenterally acceptable diluent or solvent,for example, as a solution in 1,3-butanediol. Among the acceptablevehicles and solvents that may be employed are water, Ringer's solution,and isotonic sodium chloride solution. In addition, sterile, fixed oilsare conventionally employed as a solvent or suspending medium. For thispurpose, any bland fixed oil may be employed, including synthetic mono-or diglycerides. In addition, fatty acids such as oleic acid are usefulin the preparation of injectables. Dimethyl acetamide, surfactantsincluding ionic and non-ionic detergents, and polyethylene glycols canbe used. Mixtures of solvents and wetting agents such as those discussedabove are also useful.

Suppositories for rectal administration of the compounds discussedherein can be prepared by mixing the active agent with a suitablenon-irritating excipient such as cocoa butter, synthetic mono-, di-, ortriglycerides, fatty acids, or polyethylene glycols which are solid atordinary temperatures but liquid at the rectal temperature, and whichwill therefore melt in the rectum and release the drug.

Solid dosage forms for oral administration may include capsules,tablets, pills, powders, and granules. In such solid dosage forms, thecompounds of this invention are ordinarily combined with one or moreadjuvants appropriate to the indicated route of administration. Ifadministered per os, the compounds can be admixed with lactose, sucrose,starch powder, cellulose esters of alkanoic acids, cellulose alkylesters, talc, stearic acid, magnesium stearate, magnesium oxide, sodiumand calcium salts of phosphoric and sulfuric acids, gelatin, acacia gum,sodium alginate, polyvinylpyrrolidone, and/or polyvinyl alcohol, andthen tableted or encapsulated for convenient administration. Suchcapsules or tablets can contain a controlled-release formulation as canbe provided in a dispersion of active compound in hydroxypropylmethylcellulose. In the case of capsules, tablets, and pills, the dosage formscan also comprise buffering agents such as sodium citrate, or magnesiumor calcium carbonate or bicarbonate. Tablets and pills can additionallybe prepared with enteric coatings.

For therapeutic purposes, formulations for parenteral administration canbe in the form of aqueous or non-aqueous isotonic sterile injectionsolutions or suspensions. These solutions and suspensions can beprepared from sterile powders or granules having one or more of thecarriers or diluents mentioned for use in the formulations for oraladministration. The compounds can be dissolved in water, polyethyleneglycol, propylene glycol, ethanol, com oil, cottonseed oil, peanut oil,sesame oil, benzyl alcohol, sodium chloride, and/or various buffers.Other adjuvants and modes of administration are well and widely known inthe pharmaceutical art.

Liquid dosage forms for oral administration can include pharmaceuticallyacceptable emulsions, solutions, suspensions, syrups, and elixirscontaining inert diluents commonly used in the art, such as water. Suchcompositions can also comprise adjuvants, such as wetting agents,emulsifying and suspending agents, and sweetening, flavoring, andperfuming agents.

The amount of active ingredient that can be combined with the carriermaterials to produce a single dosage form will vary depending upon thepatient and the particular mode of administration.

Doses/Quantities of Peptide Complexes

The quantity of cell membrane-permeant peptide complex comprising aradionuclide for use in radiolabelling and imaging, or relaxivity metal,should be an effective amount for the intended purpose. Such amounts canbe determined empirically, and are also well known in the art. Forexample, amounts of radio nuclide administered via the present complexescan be in the range of from about 1 μCi to about 100 mCi, preferablyfrom about 1 mCi to about 100 mCi, and more preferably from about 1 mCito about 50 mCi. This amount can be adjusted for body weight and theparticular disease state, and can be about 1 mCi/kg body weight.

For therapeutic purposes, the amount of radio nuclide administered viathe present complexes can be in the range of from about 1 mCi to about300 mCi, preferably from about 25 mCi to about 250 mCi, and morepreferably from about 50 mCi to about 200 mCi. Of course, this amountcan be tailored to meet the specific requirements of the disease statebeing treated, and can also vary depending upon the weight and conditionof the patient as is well known in the art. Note, for example, ClinicalNuclear Medicine, 1998, Third Edition, Chapman & Hall Medical.

The amount of complex comprising a drug or other pharmacologicallyactive agent for administration to a patient to treat or prevent adisease condition will vary with the type of drug, and will comprise atherapeutically effective amount thereof. Drug dosages for treatingvarious conditions are well known in the art. Note in this regard, forexample, Goodman & Gilman's The Pharmacological Basis of Therapeutics,1996, Ninth Edition, McGraw-Hill, New York.

Routes of Administration

The complexes of the present invention can be administered by a varietyof methods, including, for example, orally, enterally, mucosally,percutaneously, or parenterally. Parenteral administration is preferred,especially by intravenous, intramuscular, subcutaneous, intracutaneous,intraarticular, intrathecal, and intraperitoneal infusion or injection,including continuous infusions or intermittent infusions with pumpsavailable to those skilled in the art. Alternatively, the complexes canbe administered by means of micro-encapsulated preparations, for examplethose based on liposomes as described in European Patent Application 0213 523.

Treatment Regimens

The regimen for treating a patient with the compounds and/orcompositions of the present invention is selected in accordance with avariety of factors, including the age, weight, sex, diet, and medicalcondition of the patient, the severity of the condition, the route ofadministration, pharmacological considerations such as the activity,efficacy, pharmacokinetic, and toxicology profiles of the particularpharmacologically active compounds employed.

Administration of the drug complexes disclosed herein should generallybe continued over a period of several days, weeks, months, or years.Patients undergoing treatment with the drug complexes disclosed hereincan be routinely monitored to determine the effectiveness of therapy forthe particular disease or condition in question.

Continuous analysis of the data obtained by these methods permitsmodification of the treatment regimen during therapy so that optimalamounts of the pharmacologically active substance in the peptide complexare administered, and so that the duration of treatment can bedetermined as well. Thus, the treatment regimen/dosing schedule can berationally modified over the course of therapy so that the lowestamounts of drug compound is administered, and so that administration ofsuch compounds is continued only so long as is necessary to successfullytreat the disease or condition.

Monitoring Devices/Procedures

Detection methods useful in practicing the present invention include,but are not limited to magnetic resonance, superconducting quantuminterference device (squid), optical imaging (e.g. fluorescencetomography, NIRF imaging systems, in vivo bioluminescence, andendoscopic fluorescence), positron emission tomography, and inparticular, planar scintigraphy or single photon emission computedtomography (SPECT). Alternative methods of detection include gammacounting, scintillation counting, scanning radiograms, densitometry andfluorography. These detection methods can be employed during or after aneffective time interval for diagnosis or imaging subsequent toadministering a peptide complex of the present invention. Such effectivetime intervals are well known in the art, or can be determined byroutine experimentation employing methods such as those disclosedherein.

Although the examples hereinafter provided contain many specificities,these should not be construed as limiting the scope of the invention,but as merely providing illustrations of some of the aspects of thepresent invention.

EXAMPLE 1 Preparation of acetyl-GRKKRRQRRR-AHA-εKGC-amidetrifluoroacetate

A Tat peptide (residues 48-57, GRKKRRQRRR (SEQ ID NO: 7)) conjugate wasprepared by solid phase peptide synthesis using N-α-FMOC-protected aminoacids and standard BOP/HOBt coupling chemistry (Merifield et al.,Biochemistry 21:5020-5031, 1982; Houghten, Proc Natl Acad Sci USA82:5131-5135, 1985; Lin, et al., Biochemistry 27:5640-5645, 1988),except for the ε-Lys residue, which used an N-α-tBOC, N-ε-FMOC-Lysresidue to generate the desired peptide-based N₃S chelating group for anincoming metal (Lister-James, et al., Q J Nucl Med 41:111-118, 1997).AHA represents aminohexanoic acid as an example of a non-functionallinker between the Tat 48-57 residues and the chelating moiety. Thepeptide was amino acetylated, carboxy amidated, and deprotected bystandard methods (Merifield et al., Biochemistry 21:5020-5031, 1982;Houghten, Proc Natl Acad Sci USA 82:5131-5135, 1985; Lin, et al.,Biochemistry 27:5640-5645, 1988). The peptide was purified (>94%) bypreparative C₁₈ reversed-phase HPLC using as eluent 0.1% trifluoroaceticacid in water (0.1% TFA/H₂O) modified with 0.1% trifluoroacetic acid in90% acetonitrile/10% water (0.1% TFA/(90% CH₃CN/H₂O)) by a lineargradient (0% to 60% over 60 min) (peptide R_(t)=21 min). The identity ofthe peptide conjugate was confirmed by amino acid analysis (13proteinogenic amino acids: Glu 1; Gly 2; Cys 1; Lys 3, Arg 6) andelectrospray mass spectrometry (m/z: 1839.0; calc: C₇₄H₁₄₃N₃₇O₁₆S₁,1839.27). The sequence was confirmed as acetyl-GRKKRRQRRR-AHA-εKGC-amide((SEQ ID NO: 30).

EXAMPLE 2 Preparation of Radiolabeledacetyl-GRKKRRQRRR-AHA-εKGC-amide(Tc^(v)-99m) trifluoroacetate

The Tat peptide conjugate complex of Example 1 was labeled with Tc-99mby ligand exchange using Tc-99m-glucoheptonate as the ligand exchangereagent (Lister-James et al., J. Nucl. Med. 38:105-111, 1997). Acommercially available stannous glucoheptonate radiopharmaceutical kit(Glucoscan, DuPont Pharma, Billerica, Mass.) was reconstituted with 1.0ml of (Tc-99m)sodium pertechnetate (50 mCi) in isotonic saline obtainedby eluting a commercial radionuclide Mo-99/Tc-99m generator, and allowedto stand for 15 min at room temperature. In a small glass vial, Tatpeptide conjugate (1 mg) was dissolved in 0.9% saline (1 ml). Then,(Tc-99m)glucoheptonate (250 μl) was added and the reaction allowed toproceed at room temperature for 15 min. Radiochemical yield (>95%) ofthe oxotechnetium complex (FIG. 2) and purity (≧90%) were determined bysilica gel TLC using 15% TFA and radiometric detection(Bioscan)((Tc-99m)-peptide complex, R_(f) 0.24; (Tc-99m)-glucoheptonate,R_(f) 0.95; (Tc-99m)-TcO₄ ⁻, R_(f) 0.95).

EXAMPLE 3 Preparation ofacetyl-GRKKRRQRRR-AHA-εKGC-amide-fluorescein-maleimide trifluoroacetate

The Tat peptide conjugate of Example 1 was labeled with fluoresceinaccording to Vives et al. (J. Biol. Chem., 272:16010-16017, 1997). In asmall glass vial, Tat peptide conjugate (1 mg) was dissolved inphosphate buffered saline (pH 7.4) and reacted with 1.2 eq offluorescein maleimide dissolved in dimethylformamide for 2 hours in thedark at room temperature. The reaction was monitored by RP-HPLC at both211 nm and 440 nm. Fluorescent peptides were purified by HPLC(purity >97%) using the above gradient conditions and lyophilized in thedark. The identity of the desired fluorescein labeled peptide wasconfirmed by electrospray mass spectrometry (m/z: 2211.0).

EXAMPLE 4 Solutions for Cell Uptake Experiments

Control solution for cell uptake experiments was a modified Earle'sbalanced salt solution (MEBSS) containing (mM): 145 Na⁺, 5.4 K⁺, 1.2Ca²⁺, 0.8 Mg²⁺, 152 Cl⁻, 0.8H₂PO₄ ⁻, 0.8 SO₄ ⁻, 5.6 dextrose, 4.0 HEPES,and 1% bovine calf serum (vol/vol), pH 7.4±0.05. A 130 mM K⁺/20 mM Cl⁻solution was made by equimolar substitution of potassiummethanesulfonate for NaCl as described by Piwnica-Worms et al. (J. Gen.Physiol., 81:731-748, 1983).

EXAMPLE 5 Cell Culture

Monolayers of human epidermoid carcinoma KB 3-1 cells and thecolchicine-selected KB 8-5 and KB 8-5-11 derivative cell lines weregrown as previously described (Akiyama et al., Somatic Cell Mol. Genet.,11:117-126, 1985; Piwnica-Worms et al., Cancer Res., 53:977-984, 1993).Briefly, cells were plated in 100-mm Petri dishes containing seven 25-mmglass coverslips on the bottom and grown to confluence in DMEM (GIBCO,Grand Island, N.Y.) supplemented with L-glutamine (1%),penicillin/streptomycin (0.1%), and heat-inactivated fetal calf serum(10%) in the presence of 0, 10 and 100 ng/ml colchicine, respectively.Human Jurkat leukemia cells and Hela tumor cell lines were maintained inRPMI supplemented with 5-10% fetal calf serum, penicillin, streptomycin,and L-glutamine at 37° C. in an atmosphere of 5% CO₂ (Peng et al.,Science, 277:1501-1505,1997).

EXAMPLE 6 Cell Accumulation and Washout Studies of Tat-Peptide ConjugateMetal Complexes

Coverslips with confluent cells were used for studies of cell transportand kinetics of labeled Tat peptide conjugate complexes as previouslydescribed (Piwnica-Worms et al., Cancer Res., 53:977-984, 1993). Cellswere removed from culture media and pre-equilibrated for 15-30 secondsin control buffer. Accumulation experiments were initiated by immersingcoverslips in 60-mm glass Pyrex dishes containing 4 ml of loadingsolution consisting of MEBSS with 7 nM to 8 μM of the peptide conjugateof Example 2 (1-2 μCi/ml). Coverslips with cells were removed at varioustimes, rinsed three times in 25 ml ice-cold isotope-free solution for 8seconds each to clear extracellular spaces, and placed in 35-mm plasticPetri dishes. Cells were extracted in 1% sodium dodecylsulfate with 10mM sodium borate before protein assay by the method of Lowry (Lowry etal. J. Biol. Chem., 193:265-275, 1951) (KB cells) or by BCA analysis(pierce Chemical Co.) using bovine serum albumin as the proteinstandard. Aliquots of the loading buffer and stock solutions also wereobtained for standardizing cellular data with extracellularconcentration of each Tc-complex. Cell extracts, stock solutions, andextracellular buffer samples were assayed for gamma activity in awell-type sodium iodide gamma counter (Cobra II, Beckman). The absoluteconcentration of total Tc-complex in solution was determined from thepeptide stock solutions and specific activity of technetium, based onequations of Mo/Tc generator equilibrium (Lamson et al., J. Nucl. Med.,16:639-641, 1975).

Characterization of accumulation of Tc-99m-peptide complex was alsoperformed for nonadherent cell lines such as human Jurkat leukemia cellswith minor modifications of methods described in the literature (Boschet al., Leukemia, 11: 1131-1137, 1997). Transport experiments wereperformed in siliconized microfuge tubes and initiated by addition of732.5 μl of cells at 2-3×10⁶ cells/ml to 10 μl of buffer containingTc-99m-peptide complex and 7.5 μl of vehicle alone or of any added drugin vehicle at 100-fold the desired concentration. The tubes wereincubated in a 37° C. water bath with occasional mixing. The reactionwas terminated by centrifuging 250 μl aliquots from the reaction for 10seconds through 800 μl of a 75:25 mixture of silicon oil, density=1.050(Aldrich) and mineral oil, density=0.875 (Acros). An aliquot of theaqueous phase was obtained to normalize extracellular concentration ofthe complex to cell-associated activity, then the oil and aqueous phaseswere aspirated and the cell pellet extracted in 0.5 ml of 1% SDS, 10 mMsodium borate. For tracer washout experiments, cells were firstincubated to plateau uptake (10 min) in loading buffer (37° C.),collected by rapid centrifugation and the pellet resuspended in 50 mlMEBSS (4° C.) to clear extracellular tracer. Following another rapidspin, the cell pellet was resuspended in isotope-free MEBSS (37° C.) andthe experiment terminated as above after various times in warm washoutbuffer. Radioactivity of the cell pellet, buffers and stocks weredetermined on a gamma counter (Cobra II, 130-165 keV window) and cellprotein was determined by the BCA assay (Pierce). Transport data arereported as fmol Tc-complex (mg protein)⁻¹ (nM₀)⁻¹ as previouslydescribed, with (nM₀)⁻¹ representing total concentration of peptideconjugate in the extracellular buffer (Piwnica-Worms et al.,Circulation, 82: 1826-1838, 1990).

When exposed to radioactive Tc-99m-Tat peptide metal complex, humanJurkat leukemia cells rapidly accumulated the complex, approaching aplateau within 2 minutes (FIG. 3). Steady-state values for theTc-99m-Tat peptide metal complex in Jurkat cells was 116±3 fmol (mgprotein)⁻¹ (nM₀)⁻¹ (n=4). Given a typical cell water space of 4 μl (mgprotein)⁻¹, this would indicate an in/out ratio for the complex of ˜30,directly demonstrating that the complex is rapidly and highlyconcentrated within cells. When continuously exposed to the complex,cells were observed to maintain this plateau for at least 1 hour.

To further characterize transport of the Tc-99m-Tat peptide metalcomplex, plateau accumulation of the agent in Jurkat cells after 10minutes of incubation was determined as a function of extracellularconcentration of the radiopharmaceutical. While readily detectable atconcentrations as low as 7 nM, cell content of the Tat-complex showedevidence of concentration-saturation as extracellular concentrationsrose into the range of 8 μM (FIG. 4). Curve fitting of the datasuggested half-maximal accumulation of the complex occurred at ˜3 μM.

To further define the interactions of the complexes with-cells, Jurkatcells were incubated with Tc-99m-complexes in MEBSS buffer alone orbuffer containing 130 mM K⁺/20 mM Cl⁻ and 1 μg/ml of the potassiumionophore valinomycin. Under these conditions, electrical potentials ofthe mitochondrial membrane (ΔΨ) and plasma membrane (E_(m)) aredepolarized toward zero, eliminating the inward driving force for uptakeof hydrophobic cationic or amphipathic molecules (Piwnica-Worms et al.,Circulation, 82:1826-1838,1990). However, while the complex might becharacterized as amphipathic, net uptake of the complex underisoelectric conditions was not decreased compared to control buffer,suggesting that the mechanism of uptake was independent of membranepotential (data not shown).

Because several membrane permeant peptides have been reported to beaccumulated within cells by mechanisms related to cytoskeletal function(Elliot and O'Hare, Cell, 88:223-233, 1997), several inhibitors known toimpact microtubulin, actin microfilament and variouscytoskeletal-mediated vesicular transport pathways were tested in Jurkatcell assays. Colchicine (100 ng/ml), taxol (1 μM), nocodozole (5 μg/ml),cytochalasin D (1 μM), brefeldin A (2.5 μg/ml) and wortmannin (100 nM)each had no significant effect on net cell uptake of this Tat-peptidemetal complex, indicating that the pathway for accumulation of thisagent is by a previously uncharacterized mechanism (data not shown).Furthermore, ice-cold buffer (4° C.) only modestly inhibited netaccumulation of the complex, further pointing to a unique cell membranetranslocation pathway not highly dependent on cellular metabolism.Cellular washout of the non-functional peptide complex of Example 2which had been previously preloaded into Jurkat cells also showed veryrapid kinetics. Washout was ˜90% complete within 20 minutes (FIG. 5).This demonstrates that the majority of non-functionalized Tat peptideconjugate is not retained within cells when extracellular concentrationsof the peptide are lowered. Only a residual level of peptiderepresenting <10% of peak activity remained in a slowly exchanging orretaining compartment.

EXAMPLE 7 Fluorescence Microscopy

Exponentially growing human KB-8-5 epidermoid carcinoma cells oncoverslips were rinsed in serum-free MEBSS (37° C.) followed byincubation in serum-free MEBSS containing the fluorescein labeledTat-peptide conjugate (1 μM) at 37° C. for 15 min. Subsequently, cellson covers lips were fixed in 4% (v/v) formaldehyde in PBS at roomtemperature and then rinsed 3 times with PBS (1 min each). Cells werethen stained and mounted with anti-fading mounting medium containingpropidium iodide (1 μg/ml) following the recommended procedures of themanufacturer (Vectashield). The distribution of the fluorescence wasanalyzed on a Zeiss confocal laser fluorescence microscope equipped witha mercury lamp, oil immersion objectives and a CCD interfaced to a PC.Propidium iodide distribution was interrogated using 340-380 nmexcitation and 430 nm emission, while fluorescein distribution wasinterrogated using 450-490 nm excitation and 520 nm emission.

To localize the subcellular distribution of the Tat-peptide conjugate,uptake experiments were performed with the fluorescein derivatizedconjugate using human KB-3-1 and KB-8-5 epidermoid carcinoma cells.Confocal microscopy revealed rapid cytoplasmic and nuclear accumulationof the fluorescein derivatized conjugate at 0.5 μM extracellularconcentration of the agent. Both KB-3-1 cells (FIG. 6) and KB-8-5 cells(not shown) displayed a similar pattern and intensity of staining.Overall, the nuclear staining pattern of most fluorescent cells wassuggestive of cytosolic and nucleolar localization of the peptideconjugate (FIG. 6).

EXAMPLE 8 Preparation of Caspase-3-Cleavable Metal and FluoresceinConjugates

Caspase-3 cleavable Tat peptide conjugate was prepared by solid phasepeptide synthesis using N-α-FMOC-protected amino acids and standardBOP/HOBt coupling chemistry as in Example 1. The peptide madeincorporated a known caspase-3 cleavable sequence (DEVD) between the Tatpeptide and the chelate. As described previously in Example 1, thepeptide was amino acetylated, carboxy amidated and deprotected bystandard methods. The peptide was purified (>94%) by preparative C₁₈reversed-phase HPLC (see Example 1), and the identity of the peptideconjugate was confirmed by amino acid analysis and electrospray massspectrometry (m/z: 2412.23; calc: C₉₆H₁₇₅N₄₃O₁₈S₁, 2411.79). Thesequence was confirmed as acetyl-GRKKRRQRRR-GDEVDG-εKGC-amide (SEQ IDNO: 31).

The caspase-3 cleavable Tat peptide conjugate was labeled with Tc-99m byligand exchange using Tc-99m-glucoheptonate as the ligand exchangereagent as described in Example 2. Radiochemical yield (>95%) of theoxotechnetium and purity (>90%) were determined by silica gel TLC using15% TFA and radiometric detection (Bioscan). The (Tc-99m)-peptidecomplex showed an R_(f)=0.33, readily distinguished from(Tc-99m)-glucoheptonate (R_(f)=0.95) and (Tc-99m)-TcO₄ ⁻ (R_(f)=0.95).

The caspase-3 cleavable Tat peptide was also readily complexed with Reby ligand exchange (Lister-James et al., J. Nucl. Med. 38:105-111,1997). To 0.1 ml of a freshly prepared solution of glucoheptonate andreducing agent (200 mg (0.81 mmol) sodium α-D-glucoheptonate and 18.4 mg(0.082 mmol) tin (II) chloride dihydrate in 1 ml distilled water) wasadded 0.1 ml of a solution of ammonium perrhenate (14.9 mg (0.055 mmol)in 1 ml) and the mixture allowed to stand for 15 min at roomtemperature. To the mixture was added 1 mg of Tat peptide caspase-3cleavable conjugate and the reaction allowed to proceed at roomtemperature for 30 minutes. The conjugate was purified by RP-HPLC as inExample 1. The identity of the ReO peptide conjugate was confirmed byelectrospray mass spectrometry (m/z: 2612.0; calc: C₉₆H₁₇₂N₄₃O₁₉S₁Re₁,2611.73).

RP-HPLC analysis using the same solvent gradient system and radiometricdetection as previously described in Example 1 revealed two closelyeluting peaks for the Tc-99m complex (R_(t,1)=23.9 min; R_(t,2)=25.8min). RP-HPLC analysis and UV detection revealed two corresponding peaksfor the Re complex (R_(t,1)=21.3 min; R_(t,2)=25.8 min), againconsistent with formation of the expected isomers of the oxometalcomplexes.

The caspase-3 cleavable Tat peptide conjugate was also labeled at theC-terminal thiol of the peptide chelator with fluorescein maleimideusing the same procedure as described in Example 3. The reaction wasmonitored by RP-HPLC at both 211 nm and 440 nm. The fluorescent peptidewas purified by RP-HPLC (R_(t)=33.5 min; purity >97%) using the gradientconditions given in Example 3, and lyophilized in the dark. The identityof the desired fluorescein labeled peptide was confirmed by electrospraymass spectrometry (m/z: 2840.0).

EXAMPLE 9 Cleavage of the Caspase-3 Cleavable Linker In Vitro and InSitu

In small reaction vials, Tat peptide chelate as the fluorescein taggedconjugate of Example 8 was incubated with and without recombinant humanactive caspase-3 in commercially available reaction buffer (caspasebuffer, Invitrogen). In vial 1 was peptide conjugate in buffer withoutcaspase-3; in vial 2 was peptide conjugate with active caspase-3; and invial 3 was stock peptide conjugate. After 6 hrs of incubation to assurecompletion of the reaction, the reaction mixtures were spotted at theorigin of silica gel TLC plates, developed in 15% TFA, and analyzedunder an UV lamp. While the unreacted peptide chelate stock and peptidechelate incubated in buffer alone retained an R_(f)=0.33, peptidechelate incubated in the presence of caspase-3 resulted in disappearanceof the R_(f)=0.33 species and appearance of a peptide cleavage productwith R_(f)=0.66. These data are consistent with cleavage of the Tatpeptide conjugate at the D-G cleavage site, thereby releasing the smallmolecular weight C-terminus G-εKGC-fluorescein fragment identified nearthe solvent front on TLC. This represents direct evidence for successfulsynthesis of a caspase-3-cleavable Tat peptide imaging conjugate.

Human Jurkat leukemia cells express pro-caspase-3. Apoptosis can beinduced by pre-incubation of Jurkat cells for 5 hr in medium containingC6-ceramide, a permeant phospholipid known to activate the cell deathprogram (Herr, et al., EMBO J. 16:6200-6208, 1997; Jayadev S, et al., JBiol Chem 270:2047-2052, 1995). After pre-incubation of Jurkat cells inMEBSS buffer at 370° C. in the absence (untreated) or presence of 5 μMC6-ceramide, 1 μM of the caspase-3 cleavable fluorescein tagged Tatpeptide of Example 8 was added to the MEBSS buffer for 30 minutes.Untreated and apoptotic cells were then spun through oil (see Example 6)to clear extracellular spaces of Tat peptide, and the intact cells inthe pellet were allowed to incubate for 5 minutes at 37° C. The oil wasquickly suctioned off, the reaction terminated with cell lysis buffer(1% SDS, 10 mM sodium borate), and the cell extract centrifuged (500×gfor 10 min) to pellet debris and precipitates. The supernatant wasremoved, lyophilized overnight, and resuspended in 500 μl of water. Inuntreated cell lysates, RP-HPLC analysis at 440 nm to observefluorescein (see Example 3) showed the presence of a peak at R_(t)=33.5min, consistent with parental Tat peptide conjugate (FIG. 7). InC6-ceramide-treated cells, however, no such species was observable (FIG.7). These results demonstrate the rapid cleavage of the Tat-peptideconjugate comprising a caspase-3-reactive linker moiety in living cellsupon activation of caspase-3.

The above experiment was repeated using the Tc-99m-Tat peptide ofExample 8. Cells were treated as above except that the Tc-99m-Tatpeptide was used, and there was no washout or post-incubation period.Tc99-m and protein content were determined using published methods(Bosch et al., Leukemia 11:1131-37, 1997). Cells induced to undergoapoptosis by treatment with C6-ceramide showed enhance uptake of Tc-99m,again showing that the presence of the caspase-3 cleavable linkerresulted in identification of apoptotic cells.

EXAMPLE 10 Imaging Studies

FVB mice were anesthetized with metophane anesthesia. Tc-99m-Tat-peptidecomplex of Example 8 (125 μCi in 50 μl saline) was injected via a tailvein into mice positioned under a gamma scintillation camera (SiemensBasicam, Siemens Medical Systems, Iselin, N.J.; 5 mm pinhole collimator;20% energy window centered over 140 keV photopeak of Tc-99m). Sequentialposterior images of mice were collected at one frame/minute for 60 minwith a 128×128 matrix and corrected for radioactive decay using a PCplatform and standard commercial image analysis software. Accumulation,of Tc-99m-Tat-peptide complex was analyzed by manually drawingregions-of-interest over various organs and subtracting backgroundradioactivity determined from a region-of-interest placed adjacent tothe thorax of each mouse. No corrections were made for scatter orattenuation. Whole body distribution of the complexes are presented inpseudo gray scale images with or without a saturation cutoff filter tohighlight contrast differences in various organs.

The Tc-99m-Tat peptide initially showed a whole body microvasculardistribution, followed by rapid and abundant renal localization andexcretion. By 30 minutes post injection of the imaging agent, the onlysite of imagable radioactivity was the urinary bladder (FIG. 8). Therewas a remarkable absence of liver activity or other background activitythat would potentially interfere with the imaging of specific organtissues or tumors. This rapid distribution pattern is consistent withthe in vitro cell kinetic and localization data, but the rapidity of therenal excretion was unexpected.

Next, direct demonstration of the feasibility of imaging caspase-3activity in vivo in a living organism using gamma scintigraphy is shown.Massive hepatic apoptosis can be induced within 1-2 hours in micefollowing the intravenous injection of anti-Fas antibody (Ogasawara, etal., Nature 364:806-809; 1993; Blankenberg, et al., Proc Natl Acad SciUSA 95:6349-6354, 1998). The Fas receptor is expressed on liver, kidney,thymus, gonads and subsets of leukocytes (Ogasawara, et al., Nature364:806-809; 1993). Thus, to test the specific localization of thecaspase-3-cleavable Tc-99m-Tat peptide agent of Example 8 in organsundergoing apoptosis in vivo, a published procedure was used to imagemice following the induction of apoptosis (Blankenberg, et al., ProcNatl Acad Sci USA 95:6349-6354, 1998). FVB mice were administeredpurified hamster anti-Fas mAb by i.v. injection and allowed to recoverfor 45 minutes prior to imaging. Following metofane anesthesia, 200 μCiof Tc-99m-Tat chelate was administered by tail vein injection, and micewere immediately positioned for imaging on a gamma scintillation camera.In untreated mice, the Tc-99m-Tat peptide initially showed a whole bodydistribution, followed by rapid and abundant renal localization andexcretion, as expected. In contrast, mice pre-treated with anti-Fas mAbshowed abundant hepatic and renal retention of radioactivity 30 minutespost injection, consistent with caspase-3-induced cleavage and retentionof the imaging fragment within the target organs (FIG. 9, right). Theseimages represent the first example of imaging caspase-3 activity invivo, and demonstrate the utility of this approach in imaging with cellmembrane-permeant peptide conjugates.

EXAMPLE 11 Preparation of D-Amino Acid Containing Peptide Conjugates

Peptide conjugates were prepared by solid state peptide synthesis asdescribed in Example 1 using D N-α-FMOC-protected amino acids andstandard BOP/HOBt coupling chemistry, except for the ε-Lys residue whichused an N-α-tBOC, N-ε-FMOC-Lys to direct peptide coupling to theε-amine. Some peptides were either N-terminus acetylated orbiotinylated, and all peptides were C-terminus amidated and deprotectedby standard methods. Peptides were purified by C₁₈ reversed-phase HPLCas described in Example 1. A single HPLC peak was observed for eachpeptide conjugate. The identity of the peptide conjugates was confirmedby amino acid analysis and electrospray mass spectrometry.

The following peptide conjugates were synthesized and characterized. Thestereoisomeric identity of the membrane permeant peptide (Tat basic)domains and the chelation domains (εKGC) are indicated for each group.AHA represents aminohexanoic acid, an amino acid residue lacking achiral center used in this example as a non-functional linker betweenthe membrane permeant peptide and the metal chelation domains.

            L          L   Acetyl-GRKKRRQRRR-AHA-εKGC-amide Conjugate 1SEQ ID NO: 30  Acetyl-RKKRRQRRR-AHA-εKGC-amide Conjugate 2 SEQ ID NO: 32 Biotin-RKKRRQRRR-AHA-εKGC-amide Conjugate 3 SEQ ID NO: 32            L          D   Acetyl-GRKKRRQRRR-AHA-εKGC-amide Conjugate 4 Acetyl-RKKRRQRRR-AHA-εKGC-amide Conjugate 5 NH₂-GRKKRRQRRR-AHA-εKGC-amide Conjugate 6  NH₂-RKKRRQRRR-AHA-εKGC-amide Conjugate 7             D          D  Acetyl-GRKKRRQRRR-AHA-εKGC-amide Conjugate 8 Acetyl-RKKRRQRRR-AHA-εKGC-amide Conjugate 9 NH₂-GRKKRRQRRR-AHA-εKGC-amide Conjugate 10  NH₂-RKKRRQRRR-AHA-εKGC-amide Conjugate 11             D          L  Acetyl-RKKRRQRRR-AHA-εKGC-amide Conjugate 12Biotin-RKKRRQRRR-AHA-εKGC-amide Conjugate 13             D         D  Biotin-RAARRAARR-AHA-εKGC-amide Conjugate 14

The conjugates identified in Table 2 were prepared by solid-phasepeptide synthesis using L- or D-N-α-FMOC-protected amino acids asindicated and standard BOP/HOBt coupling chemistry as is known in theart, with the exception that N-ε-FMOC-protected Lys (*K) was used in thechelation sequence to direct orthogonal peptide coupling and free theα-amino for coordination with the incoming metal. Peptides were purified(>94%) by preparative C₁₈ reverse-phase HPLC, and single HPLC peaks wereobserved for each peptide conjugate. The identity of all peptides wasconfirmed by amino acid analysis and electrospray mass spectrometry asis known in the art.

EXAMPLE 12 Preparation of [99 mTc^(v)O Tat-Peptide Trifluroracetate

The Tat-peptide conjugates prepared in Example 11 were labeled with^(99m)Tc by ligand exchange using [^(99m)Tc] glucoheptonate as describedin Example 2.

EXAMPLE 13 Preparation of [Re^(v)O] Tat-Peptide Trifluoroacetate

The Tat-peptide conjugates prepared in Example 11 were also reacted withRe by ligand exchange using [Re]glucohemtoanate as the ligand exchangereagent by the method used in Example 2. To 0.1 ml of a freshly preparedsolution of 0.81 mmol sodium α-D-glucoheptonate and 0.082 mmol tin(II)chloride dihydrate was added 0.1 ml of a solution of 0.055 mmol ammoniumperrhenate and the mixture allowed to stand for 15 minutes at roomtemperature. To the mixture was added 1 mg of the Tat-peptide conjugate(0.41 μmol) in water and the reaction allowed to proceed at roomtemperature for 30 minutes. Reversed phase HPLC analysis was performedas previously described and the desired fractions collected. Theidentity of the isolated [Re]Tat-peptide complexes was confirmed byelectrospray mass spectrometry.

EXAMPLE 14 Cellular Uptake and Washout Studies of [^(99m)Tc]D-Tat-Peptide Conjugates

Control solution for the cellular uptake experiments was the modifiedEarle's balanced salt solution (MEBSS) described in Example 4.

Kinetic experiments of [^(99m)Tc]D-Tat-peptide complexes were performedin Jurkat leukemia cells suspended in MEBSS with minor modification ofthe methods described in Example 6. Transport experiments were performedin siliconized microfuge tubes and initiated by addition of 732.5 μl ofcells at 2-3×10⁶ cells/ml to 10 μl of MEBSS containing[^(99m)Tc]D-Tat-peptide complex and 7.5 μl of vehicle alone or of anyadded drug in vehicle at 100 fold the desired concentration. Unlessstated otherwise, [^(99m)Tc]D-Tat-peptide complex was added to MEBSSaccompanied by a molar excess of unlabeled D-Tat-peptide as obtaineddirectly from the labeling procedure. The final total peptideconcentration was 7 nM to 8 μM (1-2 μCi/ml). The tube were incubated at37° C. and the reaction terminated as previously described. For peptidewashout experiments, cells were first incubated to plateau uptake (20minutes) in MEBSS loading buffer at 37° C., collected by rapidcentrifugation and the pellet resuspended in 50 ml of isotope-free MEBSSat 4° C. to clear extracellular tracer. Following another rapid spin,the cell pellet was resuspended in isotope-free MEBSS at 37° C. forvarious times and the reaction terminated as described previously.Protein assays and determination of gamma activity were as described inExample 6. Absolute concentration of total [Tc]Tat-peptide complex insolution was determined from the specific activity of Tc, based onequations of Mo/Tc generator equilibrium (Lamson et al., J. Nucl. Med.,16:639-641, 1975). Transport data are reported as pmol of peptide_(i)(mgprotein)⁻¹ (μM₀)⁻¹, wherein peptide_(i) represents total peptideconjugate within the cells and (nM₀)⁻¹ represents concentration of totalpeptide conjugate in the extracellular buffer.

As shown in Table 1, stereoisomeric substitution of D amino acids in themetal chelation motif resulted in no significant change in overallaccumulation levels in Jurkat cells. Neither deletion of the N-terminusGly (Conjugates 5 and 7) nor deletion of the N-terminus acetyl(Conjugates 6 and 7) conferred any significant differences in overallcell penetration.

Conversely, peptide conjugates synthesized by solid phase methods withall D-amino acids comprising both the -εKGC chelation motif and themembrane permeant domain (Conjugates 8-11), showed an 8 to 9-foldincreased accumulation. Again, neither deletion of the N-terminus Gly(Conjugates 9 and 11) nor deletion of the N-terminus acetyl (Conjugates10 and 11) conferred any significant differences in the overall enhancedlevels of cell penetration.

Direct proof that this stereospecific enhancement of membranepenetration was conferred by the membrane permeant domain was obtainedby synthesis of mixed peptides where natural L-amino acids comprised the-εKGC chelation motif and D-peptides comprised the membrane permeantdomain (Conjugates 12 and 13). These mixed peptides also showed 8- to9-fold increased accumulation in Jurkat cells (Table 1). Neitherdeletion of the N-terminus Gly (Conjugate 12) nor substitution of theN-terminus acetyl with biotin (Conjugate 13) conferred any significantdifferences in the overall enhanced levels of cell penetration. Therewas a minor trend for the D peptides to show slightly greater residualactivity remaining within the cell 30 minutes after a wash inisotope-free buffer (Table 1). However, the net gain in cell uptakeconferred by the D peptide permeation motif far exceeded this slightincrease in residual binding as shown by the enhanced uptake/washout(U/W) ratios for the D peptides. Further demonstration of the importanceof the specific D sequences identified by these experiments is shown bycomparison to another highly basic all D peptide (Conjugate 14). Thisall D peptide was no different than the native Tat peptide chelate(Conjugate 1) in overall cell uptake (Table 1). Direct comparative dataof cell uptakes of peptide conjugates comprising various combination ofstereoisomers of the permeation/chelation motifs (L/L; L/D; D/D; andD/L) are shown in FIG. 10. These data reinforce the large andunanticipated enhancement of cellular accumulation of[^(99m)Tc]Tat-peptide complexes conferred by the use of D-amino acidsfor synthesis of the membrane permeant domain.

EXAMPLE 15 Preparation of [^(99m)Tc(CO)₃] Peptides

N-terminus His tagged peptide conjugates were labeled with[^(99m)Tc(CO)₃] for the conjugate numbers 39, 40, 41, 42 of Table 2using a commercially available tricarbonyl radiopharmaceutical kit(K₂BH₃CO₂, 4 mg; K₂B₄O₇.H₂O, 10 mg; NaK tartrate, 10 mg; pH 10;Mallinckrodt, Inc., St. Louis, Mo.) Kits were reconstituted with 1.0 mLof [^(99m)Tc]Na(TcO₄) (20-40 mCi) in isotonic saline obtained by elutinga commercial ⁹⁹Mo/^(99m)Tc generator, and allowed to react in a 100° C.oil bath for 10-15 minutes. Following neutralization with 80 μL of 1NHCl, 90 μL of the [^(99m)Tc(CO)₃(H₂O)₃]⁺ solution was added to 10 μL ofa stock peptide solution and allowed to react for 20 min at 85-90° C.Radiochemical yields (>95%) of [^(99m)Tc(CO)₃]Tat-peptide complexes weredetermined by TLC using silica gel developed with either 68% MeOH/30%saline/2% TFA or H₂O and scanning radiometric detection. Radiochemicalpurity (>90%) was determined by radiometric RP-HPLC using the solventgradient system described above.

EXAMPLE 16 Cellular Uptake as Related to Substitution at Position −4from C-Terminus of Peptide

Residue 55 (Gln) of the Tat basic domain has been hypothesized to conferbinding to TAR RNA. Several different amino acids were substituted inthe corresponding residue in the D-Tat basic domain (RKKRRXRRR) todetermine the contribution of Gln to net cellular uptake. As shown inFIG. 12A, significant differences in net cell uptakes were observed withsingle amino acid substitutions at this position. The substitutions leadto enhanced cell uptake in the following order: Glu<Gln<Asn<NorLeu<Orn.When a similar series of substitutions was performed on the D poly-Arg₈peptide at the analogous position, all substitutions decreased cellularuptake (FIG. 12B).

It is to be understood that the present invention has been described indetail by way of illustration and example in order to acquaint othersskilled in the art with the invention, its principles, and its practicalapplication. Particular formulations and processes of the presentinvention are not limited to the descriptions of the specificembodiments presented, but rather the descriptions and examples shouldbe viewed in terms of the claims that follow and their equivalents.While some of the examples and descriptions above include someconclusions about the way the invention may function, the inventor doesnot intend to be bound by those conclusions and functions, but puts themforth only as possible explanations.

It is to be further understood that the specific embodiments of thepresent invention as set forth are not intended as being exhaustive orlimiting of the invention, and that many alternatives, modifications,and variations will be apparent to those skilled in the art in light ofthe foregoing examples and detailed description. Accordingly, thisinvention is intended to embrace all such alternatives, modifications,and variations that fall within the spirit and scope of the followingclaims.

TABLE 1 Stereoisomer #Amino Tat Peptide Chelate 20 min 30 min ConjugateAcids N-term Domain Domain Uptake SEM Washout SEM U/W Ratio 1 14 Ac, GlyL L 77.93 3.47 24.26 7.63 3.2 2 13 Ac L L 61.73 6.05 10.99 1.84 5.6 3 13Biotin L L 42.74 3.15 24.32 6.28 1.8 4 14 Ac, Gly L D 68.58 5.76 22.930.50 3.0 5 13 Ac L D 46.75 3.65 24.52 1.53 1.9 6 14 Gly L D 106.96 1.5540.19 2.72 2.7 7 13 L D 64.35 1.63 26.84 2.52 2.4 8 14 Ac, Gly D D317.92 21.29 50.87 14.76 6.2 9 13 Ac D D 357.91 28.00 42.99 2.01 8.3 1014 Gly D D 314.02 61.48 55.67 1.59 5.6 11 13 D D 236.81 13.37 61.92 5.483.8 12 13 Ac D L 326.99 8.89 46.03 4.43 7.1 13 13 Biotin D L 387.2524.42 36.22 5.16 10.7 14 13 Biotin D D 58.81 5.85 17.45 0.77 3.4

TABLE 2 Congugate Mol. Perm. Seq. Chelation Jurkat Cell No. WeightSequence Chirality Chirality Uptake  1a 1839.0Ac-GRKKRRQRRR-AHA-K*GC-amide L L  92.90 ± 21.17  2b 1839.3Ac-GRKKRRQRRR-AHA-k*gc-amide L D  50.39 ± 25.73  3c 1839.3Ac-grkkrrqrrr-AHA-k*gc-amide D D 256.97 ± 86.20  4d 1782.2Ac-RKKRRQRRR-AHA-K*GC-amide L L  90.75 ± 41.04  5e 1782.2Ac-RKKRRQRRR-AHA-k*gc-amide L D  48.81 ± 2.91  6f 1782.2Ac-rkkrrqrrr-AHA-K*GC-amide D L 300.10 ± 38.04  7g 1782.2Ac-rkkrrqrrr-AHA-k*gc-amide D D 340.35 ± 164.68  8h 1740.2RKKRRQRRR-AHA-k*gc-amide L D  64.35 ± 1.63  9i 1740.2Rkkrrqrrr-AHA-k*gc-amide D D 236.81 ± 13.37 10j 1797.2GRKKRRQRRR-AHA-k*gc-amide L D 106.96 ± 1.55 11k 1797.2Grkkrrqrrr-AHA-k*gc-amide D D 314.02 ± 61.48 12l 1965.5Biotin-RKKRRQRRR-AHA-K*GC-amide L L  51.07 ± 11.78 13m 1965.5Biotin-rkkrrqrrr-AHA-K*GC-amide D L 426.26 ± 96.33 14n 1809.3Biotin-kkrrqrrr-AHA-K*GC-amide D L 221.38 ± 27.51 15 1681.1Biotin-krrqrrr-AHA-K*GC-amide D L 129.57 ± 24.99 16 1552.9Biotin-kkqrrr-AHA-K*GC-amide D L  76.57 ± 3.30 17 1396.7Biotin-rqrrr-AHA-K*GC-amide D L  51.37 ± 15.08 18 1297.6Biotin-rraarr-k*gc-amide D D  71.48 ± 10.32 19 1368.7Biotin-arraarr-k*gc-amide D D  51.19 ± 20.69 20 1439.8Biotin-aarraarr-k*gc-amide D D  49.98 ± 13.36 21 1595.9Biotin-raarraarr-k*gc-amide D D  66.48 ± 10.85 22 1768.2Ac-rkkrr-n-rrr-AHA-k*gc-amide D D 528.64 ± 157.11 23 1768.2Ac-rkkrr-orn-rrr-AHA-k*gc-amide D D 942.24 ± 102.99 24 1783.2Ac-rkkrr-e-rrr-AHA-k*gc-amide D D 252.80 ± 62.26 25 1767.2Ac-rkkrr-norleu-rrr-AHA-k*gc-amide D D 609.21 ± 39.36 26 1397.7Ac-RRRRRR-AHA-k*gc-amide L D  28.03 ± 18.97 27 1397.7Ac-rrrrrr-AHA-k*gc-amide D D 130.32 ± 29.01 28 1553.9Ac-RRRRRRR-AHA-k*gc-amide L D  34.73 ± 6.99 29 1553.9Ac-rrrrrrr-AHA-k*gc-amide D D 307.95 ± 34.80 30 1710.1Ac-RRRRRRRR-AHA-k*gc-amide L D  59.02 ± 5.52 31 1710.1Ac-rrrrrrrr-AHA-k*gc-amide D D 781.60 ± 266.98 32 1866.3Ac-RRRRRRRRR-AHA-k*gc-amide L D 129.11 ± 69.01 33 1866.3Ac-rrrrrrrrr-AHA-k*gc-amide D D 861.68 ± 349.61 34 1668.0Ac-rrrr-n-rrr-AHA-k*gc-amide D D 297.72 ± 119.04 35 1668.0Ac-rrrr-orn-rrr-AHA-k*gc-amide D D 532.24 ± 43.18 36 1683.0Ac-rrrr-e-rrr-AHA-k*gc-amide D D 215.38 ± 16.00 37 1667.1Ac-rrrr-norleu-rrr-AHA-k*gc-amide D D 324.24 ± 31.95 38 1731.1Ac-plssifsrigdp-AHA-k*gc-amide D D  21.26 ± 0.72 39 1532.8hg-rkkrrqrrr-amide D D 888.71 ± 54.81 40 1636.0 hgc-rkkrrqrrr-amide D D472.19 ± 59.06 41 1693.0 hg-rkkrrqrrr-gc-amide D D 542.76 ± 4.07 421882.3 hg-rkkrrqrrr-gk(Dde)-amide D D 607.21 ± 12.77 a Abbreviations: *,K,ε-amino peptide coupling; AHA, amino hexanoic acid; Ac, N-terminusacetyl modified; biotin, N-terminus biotinylated; amide, C-terminusamido modified; Orn, ornithine; Norleu, norleucine; Dde,1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl. In this table, lowercasedesignations indicate D-amino acids and upper case indicates L-aminoacids.

1. A compound, comprising: a cell membrane-permeant peptide consistingof a peptide sequence selected from the group consisting of SEQ ID NO:6, SEQ ID NO: 7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ IDNO: 36; a diagnostic or pharmaceutically active substance; and anon-functional linker moiety linking said peptide and said diagnostic orpharmaceutically active substance; wherein said cell membrane-permeantpeptide comprises at least one D-amino acid, or a pharmaceuticallyacceptable salt of said compound.
 2. The compound of claim 1, whereinthe majority of the amino acids comprising said cell membrane-permeantpeptide are D-amino acids.
 3. The compound of claim 2, wherein said cellmembrane-permeant peptide is comprised entirely of D-amino acids.
 4. Thecompound of claim 1 wherein said cell membrane-permeant peptide is ofSEQ ID NO:
 6. 5. The compound of claim 1 wherein said non-functionallinker moiety is selected from the group consisting of amino hexanoicacid, glycine, alanine, peptide chains of nonpolar amino acids, andhydrocarbon chains.
 6. The compound of claim 1 wherein said diagnosticsubstance is selected from the group consisting of a radionuclide, arelaxivity metal, a fluorochrome, a dye, and an enzyme substrate.
 7. Thecompound of claim 6, wherein said radionuclide or relaxivity metal iscoordinated to a chelation ligand linked to said non-functional linkermoiety.
 8. The compound of claim 7, wherein said chelation ligand isselected from the group consisting of DTPA, EDTA, and DOTA.
 9. Thecompound of claim 8, wherein said radionuclide is a radioactive isotopeof a metal selected from the group consisting Tc, Ru, In, Ga, Co, Pt,Fe, Os, Ir, W, Re, Cr, Mo, Mn, Ni, Rh, Pd, Nb, Cu, and Ta.
 10. Thecompound of claim 9, wherein said relaxivity metal is a paramagneticisotope of a metal selected from the group consisting of Mn, Cr, Fe, Gd,Eu, Dy, Ho, Cu, Co, Ni, Sm, Tb, Er, Tm, and Yb.
 11. A composition,comprising a compound comprising: a cell membrane-permeant peptideconsisting of a peptide sequence selected from the group consisting ofSEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35,and SEQ ID NO: 36; a diagnostic or pharmaceutically active substance;and a non-functional linker moiety linking said peptide and saiddiagnostic or pharmaceutically active substance; wherein said compoundfurther comprises at least one D-amino acid.
 12. The composition ofclaim 11, further comprising a pharmaceutically acceptable carrier,excipient, or diluent.
 13. The composition of claim 12, wherein themajority of amino acids comprising said compound are D-amino acids. 14.The composition of claim 13, wherein said membrane permeant peptide iscomprised entirely of D-amino acids.
 15. A kit, comprising a compoundcomprising: a cell membrane-permeant peptide consisting of a peptidesequence selected from the group consisting of SEQ ID NO: 6, SEQ ID NO:7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; ametal chelation ligand; and a non-functional linker moiety linking saidpeptide and said metal chelation ligand; wherein said compound furthercomprises at least one D-amino acid; and a reducing agent capable ofreducing a metal that can be coordinately incorporated into said metalchelation ligand.
 16. A method for imaging cells in vivo, comprising:administering to an animal a cell imaging effective amount of a compoundcomprising: a cell membrane-permeant peptide consisting of a peptidesequence selected from the group consisting of SEQ ID NO: 6, SEQ ID NO:7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; achelated radionuclide or a chelated relaxivity metal; and non-functionallinker moiety linking said peptide and said chelated radionuclide orsaid chelated relaxivity metal, wherein said compound further comprisesat least one D-amino acid; and monitoring the location of saidradionuclide or relaxivity metal within said animal.
 17. A method fordetecting cellular apoptosis in viva comprising: administering to ananimal a cellular apoptosis detecting effective amount of a compoundcomprising: a cell membrane-permeant peptide consisting of a peptidesequence selected from the group consisting of SEQ ID NO: 6, SEQ ID NO:7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; adiagnostic substances; a non-functional linker moiety linking thepeptide and the diagnostic substance, wherein said compound furthercomprises at least one D-amino acid and said diagnostic substance isreactive with caspase; and monitoring the diagnostic substance withinthe animal.
 18. A method for detecting an enzyme in a cell comprising:contacting the cell with an enzyme detecting effective amount of acompound comprising: a cell-permeant peptide consisting of a peptidesequence selected from the group consisting of SEQ ID NO: 6, SEQ ID NO:7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; adiagnostic substance; a non-functional linker moiety linking the peptideand the diagnostic substance, wherein said compound further comprises atleast one D-amino acid and said diagnostic substance is reactive withthe enzyme; removing unreacted compound from the locus of the cell sothat the signal to noise ratio is sufficient for diagnostic purposes;and monitoring the presence of the diagnostic substance in the cell. 19.A method for delivering a pharmaceutically active substance to a cellcomprising, contacting the cell with an effective amount of a compoundcomprising: a cell-membrane permeant peptide consisting of a peptidesequence selected from the group consisting of SEQ ID NO: 6, SEQ ID NO:7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; apharmaceutically active substance; and a non-functional linker moietylinking the peptide and the pharmaceutically active substance; whereinsaid compound further comprises at least one D-amino acid.
 20. A methodfor assessing the effect of a drug in altering the expression oractivity of an enzyme in a target cell, comprising: contacting thetarget cell with a diagnostically effective amount of a compoundcomprising: a cell membrane-permeant peptide consisting of a peptidesequence selected from the group consisting of SEQ ID NO: 6, SEQ ID NO:7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; adiagnostic substance; a non-functional linker moiety linking the peptideand the diagnostic substance; wherein the compound further comprises atleast one D-amino acid clearing unreacted compound from the locus of thecell so that the signal to noise ratio is sufficient for diagnosticpurposes; and monitoring or evaluating the diagnostic substance in thetarget cell.
 21. The compound of claim 1, wherein said cellmembrane-permeant peptide comprises amino acids selected from the groupconsisting of proteogenic amino acids and non-proteogenic amino acids.22. The compound of claim 1 wherein said cell membrane-permeant peptideis SEQ ID No:
 7. 23. The compound of claim 6, wherein said radionuclideis a radioactive isotope of a metal selected from the group consistingof Tc-m99 , In-111, Ga-67, Ga-68, Cu-64, Ru-97, Cr-51, Co-57, Re-188,and Re-186.
 24. The composition of claim 11, wherein said compositioncomprises from about 1 μCi to about 100 mCi of said compound when saidcompound is conjugated to a radionuclide.
 25. The composition of claim12, wherein said composition comprises about from about 1 mCi to about50 mCi when said compound is conjugated to a radionuclide.
 26. Thecompound of claim 4, wherein said membrane-permeant peptide comprises atleast one D-amino acid.
 27. The compound of claim 4, wherein themajority of the amino acids comprising said membrane-permeant peptideare D-amino acids.
 28. The compound of claim 4, wherein saidmembrane-permeant peptide is comprised of D-amino acids.
 29. A methodfor imaging cells in vivo, comprising: administering to an animal a cellimaging effective amount of a compound comprising: a cellmembrane-permeant peptide consisting of a peptide sequence selected fromthe group consisting of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 33, SEQID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; a chelated radionuclide ora chelated relaxivity metal; and a functional linker moiety linking saidpeptide and said chelated radionuclide or said chelated relaxivitymetal, wherein said functional linker confers target cell specificity tosaid compound, and monitoring the location of said radionuclide orrelaxivity metal within said animal.
 30. A method for detecting cellularapoptosis in vivo comprising: administering to an animal a cellularapoptosis detecting effective amount of a compound comprising: a cellmembrane-permeant peptide consisting of a peptide sequence selected fromthe group consisting of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 33, SEQID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; a diagnostic substances; afunctional linker moiety linking the peptide and the diagnosticsubstance, wherein the functional linker moiety comprises acaspase-reactive sequence; and monitoring the diagnostic substancewithin the animal.
 31. A method for detecting an enzyme in a cellcomprising: contacting the cell with an enzyme detecting effectiveamount of a compound comprising: a cell-permeant peptide consisting of apeptide sequence selected from the group consisting of SEQ ID NO: 6, SEQID NO: 7, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO:36; a diagnostic substance; a functional linker moiety linking thepeptide and the diagnostic substance, wherein the functional linkermoiety comprises a sequence reactive with the enzyme; removing unreactedcompound form the locus of the cell so that the signal to noise ratio issufficient for diagnostic purposes; and monitoring the presence of thediagnostic substance in the cell.
 32. A method for delivering apharmaceutically active substance to a cell comprising, contacting thecell with an effective amount of a compound comprising: a cell-membranepermeant peptide consisting of a peptide sequence selected from thegroup consisting of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 33, SEQ IDNO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; a pharmaceutically activesubstance; and a functional linker moiety linking the peptide and thepharmaceutically active substance; wherein said compound furthercomprises at least one D-amino acid and said functional linker moietyconfers target cell specificity to the compound.
 33. A method forassessing the effect of a drug in altering the expression or activity ofan enzyme in a target cell, comprising: contacting the target cell witha diagnostically effective amount of a compound comprising: a cellmembrane-permeant peptide consisting of a peptide sequence selected fromthe group consisting of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 33, SEQID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; a diagnostic substance; afunctional linker moiety linking the peptide and the diagnosticsubstance; wherein the functional linker moiety confers target cellspecificity to the compound, and which comprises a sequence capable ofinteracting with the enzyme so as to release the diagnostic substancefrom the compound into the interior of the cell; clearing unreactedcompound from the locus of the cell so that the signal to noise ratio issufficient for diagnostic purposes; and monitoring or evaluating thediagnostic substance in the target cell.
 34. A compound, comprising: acell membrane-permeant peptide consisting of a peptide sequence selectedfrom the group consisting of SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 33,SEQ ID NO: 34, SEQ ID NO: 35, and SEQ ID NO: 36; a diagnostic orpharmaceutically active substance; and a functional linker moietylinking said peptide and said diagnostic or pharmaceutically activesubstance, wherein said functional linker moiety confers target cellspecificity to said compound and said permeant peptide comprises atleast one positively charged amino acid, or a pharmaceuticallyacceptable salt of said compound.
 35. The compound of claim 34 whereinsaid permeant peptide comprises a majority of positively charged aminoacids.
 36. The compound of claim 35 wherein said permeant peptide iscomprised entirely of positively charged amino acids.
 37. The compoundof claim 36 wherein said permeant peptide comprises a majority ofD-amino acids.
 38. The compound of claim 1 wherein the sequence of saidpeptide comprises at least one modification to increase the cationiccharge of the permeant peptide.
 39. The compound of claim 1, whereinsaid cell membrane-permeant peptide is selected from the groupconsisting of the permeant peptide of SEQ ID NO: 33, the permeantpeptide of SEQ ID NO: 34, the permeant peptide of SEQ ID NO: 35, and thepermeant peptide of SEQ ID NO:
 36. 40. The peptide conjugate of claim39, wherein said peptide conjugate comprises at least one D-amino acid.41. The compound of claim 39, wherein the majority of the amino acidscomprising said membrane-permeant peptide are D-amino acids.
 42. Thecompound of claim 39, wherein said membrane-permeant peptide iscomprised of D-amino acids.
 43. A compound, comprising: a cellmembrane-permeant peptide; a diagnostic or pharmaceutically activesubstance; and a functional linker moiety linking said peptide and saiddiagnostic or pharmaceutically active substance, wherein said functionallinker moiety confers target cell specificity to said compound and saidpermeant peptide consists of a peptide sequence selected from the groupconsisting of SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, and SEQ IDNO: 36, or a pharmaceutically acceptable salt of said compound.